January 2023
Which statement describes the changes in bonding and energy that occur when a molecule of iodine, I2, forms two separate atoms of iodine?
(1) A bond is formed as energy is absorbed.
(2) A bond is formed as energy is released.
(3) A bond is broken as energy is absorbed.
(4) A bond is broken as energy is released.
Solution: When a molecule of iodine I2 is broken into two atoms of iodine, the bond is broken. Breaking a bond means energy must be absorbed.
Answer: Choice 3 is correct.
16 The particles in which sample have the lowest average kinetic energy?
(1) 50. g of sulfur at 273 K
(2) 40. g of aluminum at 298 K
(3) 30. g of sulfur at 303 K
(4) 20. g of aluminum at 323 K
Solution: Temperature is the measure of the average kinetic energy. Since choice 1 has the lowest temperature, it should have the lowest average kinetic energy as well.
Answer: 1
18 Which equation represents a physical equilibrium?
Solution:
A physical equilibrium is represented by an equation where the two phases are in equilibrium with one another. Two opposite facing arrows represent an equilibrium. This eliminates choices 1 and 3. Choice 4 represents an equilibrium between the liquid(l) and gas(g) phases and is the correct answer.
Answer: 4
19 Systems in nature tend to undergo changes toward
(1) higher energy and higher entropy
(2) higher energy and lower entropy
(3) lower energy and higher entropy
(4) lower energy and lower entropy
Solution: Entropy represents disorder. System undergoes changes to increase disorder (higher entropy). Also, lower energy means more stable system. Choice 3 is correct, lower energy and higher entropy.
Answer: 3
43 Based on Table I, which chemical equation represents a reaction with a heat of reaction that indicates a net release of energy?
(1) N2(g) + O2(g) → 2NO(g)
(2) N2(g) + 2O2(g) → 2NO2(g)
(3) 2C(s) + 3H2(g) → C2H6(g)
(4) 2C(s) + 2H2(g) → C2H4(g)
Solution: When ΔH has a positive sigh the reaction is endothermic (heat is absorbed). When ΔH has a negative sign, the reaction is exothermic (heat is released). Therefore, we are looking for a reaction with a negative ΔH sign.
Answer: Choice 3 is the correct answer.
44 The greatest increase in entropy occurs when a 1.00-gram sample of water changes from
(1) solid to liquid
(2) solid to gas
(3) gas to liquid
(4) liquid to solid
Solution:Entropy represents disorder. Disorder increases going from solid to liquid to gas. Solid to gas results in the greatest increase in entropy.
Answer: Choice 2 is the correct answer choice.
August 2022
12. When an atom of hydrogen and an atom of chlorine combine to form a molecule of hydrogen chloride, a bond is
(1) formed as energy is absorbed
(2) formed as energy is released
(3) broken as energy is absorbed
(4) broken as energy is released
Solution:When two atoms combine, a bond must form between them. Forming a bond releases energy.
Answer: 2
18. Which form of energy is converted to thermal energy when propane burns in air?
(1) chemical
(2) electrical
(3) mechanical
(4) nuclear
Solution: Chemical energy is energy stored inside a molecule such as propane and can be used and converted to thermal energy when propane is burned.
Answer: 1
19. According to the kinetic molecular theory, which statement explains why an ideal gas can be compressed to a smaller volume?
(1) The motion of the gas particles is circular and orderly.
(2) The force of attraction between the gas particles is strong.
(3) As the gas particles collide, the total energy of the system decreases.
(4) The gas particles are separated by great distances relative to their size.
Solution: Kinetic molecular theory has the following statements which need to be memorized:
Gas particles have negligible volume.
The gas particles are in continuous random motion and move in straight lines.
No forces of attraction or repulsion are considered to exist between the particles.
Collisions of gas particles may transfer energy from one particle to another, but the total kinetic energy remains the same.
Answer: 4
23. What is the purpose of adding a catalyst to a chemical reaction?
1. to decrease the potential energy of the products
2. to increase the potential energy of the reactants
3. to convert solid reactants to liquid reactants
4. to provide an alternate reaction pathway
Solution: A catalyst is a substance that speeds up the reaction by lowering its activation energy. How does it lower activation energy? By providing an alternate reaction pathway.
Answer: 4
24. Systems in nature tend to undergo changes toward
(1) lower energy and less disorder
(2) lower energy and greater disorder
(3) higher energy and less disorder
(4) higher energy and greater disorder
Solution: In nature, changes occur to increase the disorder (entropy) and to lower the energy (enthalpy).
Answer: 2
43. Which statement describes ice and liquid water in a stoppered flask at 0°C at equilibrium?
(1) The rate of melting must equal the rate of freezing.
(2) The rate of freezing must be greater than the rate of melting.
(3) The mass of the ice must equal the mass of the liquid water.
(4) The mass of the ice must be greater than the mass of the liquid water.
Solution: At equilibrium the rates of forward and reverse reactions are equal. Ice can turn into liquid in a process called melting and back from liquid water into ice in a process called melting.
Answer: 1
44. Given the equation representing a system at equilibrium in a sealed, rigid container:
N2(g) + O2(g) + 182.6 kJ ⇌ 2NO(g)
When heat is added to the system, the concentration of N2(g)
(1) decreases and the concentration of NO(g) decreases
(2) decreases and the concentration of NO(g) increases
(3) increases and the concentration of NO(g) increases
(4) increases and the concentration of NO(g) decreases
Solution: This question tests our knowledge of Le Chatelier's principle. We see energy, 182.6 kJ on the reactant side (left). We can treat it as a reactant. When heat is added, there will be too much heat on the left side and to relieve this, the equilibrium will need to shift to the opposite side (right). If equilibrium shifts to the right, everything on the right will increase (concentration of NO) and everything on the left will decrease (concentration of N2)
Answer: 2
June 2022
20. A collision between reactant particles is most likely to result in a reaction when the particles have proper orientation and proper
(1) charge
(2) energy
(3) mass
(4) radius
Solution:: This one just needs to be memorized. In order for reactant molecules to collide effectively and product products, they need to have proper orientation and energy.
Answer: 2
21. Given the equation representing a system at equilibrium: 2NO2(g) ⇌ N2O4(g)
Which statement describes this reaction at equilibrium?
1. The concentration of the reactant and the product must be equal.
2. The concentration of the reactant and the product must be constant.
3. The rates of the forward and reverse reactions are increasing.
4. The rates of the forward and reverse reactions are decreasing.
Solution:: There are two facts that we need to memorize about a reaction at equilibrium. First, at equilibrium the rate of forward and reverse reactions are equal. Secondly, the concentration of reactants and products will remain constant.
Answer: 2
22 Which phrase describes the effect of adding a catalyst to a chemical reaction in order to increase the reaction rate?
(1) provides a different reaction pathway with a lower activation energy
(2) provides a different reaction pathway with a higher activation energy
(3) uses the same reaction pathway with a higher activation energy
(4) uses the same reaction pathway with a lower activation energy
Solution:: A catalyst is a substance that increase the rate of the reaction by lowering the activation energy.
Answer: 1
23. Systems in nature tend to undergo changes toward
(1) lower energy and less disorder
(2) lower energy and greater disorder
(3) higher energy and less disorder
(4) higher energy and greater disorder
Solution: Systems in nature want to undergo changes to lower energy and increase the disorder (entropy)
Answer: 2
42 Given the equation representing a system at equilibrium: 2SO2(g) + O2(g) ⇌ 2SO3(g) + energy
Which change favors the forward reaction?
(1) increasing the concentration of O2(g)
(2) increasing the temperature
(3) decreasing the pressure
(4) decreasing the concentration of SO2(g)
Solution:: This question is about Le Chatelier's principle. Let's look at the answer choices. Increasing the concentration of O2(g), means we have too much O2, and equilibrium should shift to the opposite side to get rid of it. O2 is on the left, and the equilibrium will shift to the right favoring forward reaction.
Answer: 1
43 When ice, H2O(s), melts at 0°C, entropy increases because the
(1) average kinetic energy of the particles increases
(2) average kinetic energy of the particles decreases
(3) particle arrangement is more random
(4) particle arrangement is less random
Solution: When ice melts turning into water, the phase change that occurs is from solid phase (ice) into a liquid phase (water). In a solid phase particles are very close to one another in a structures arrangement. In a liquid phase, particles are further away from one another and are more randomly arranged. Kinetic energy does not change during a phase change.
Answer: 3
January 2020
12 Which statement describes the particles of an ideal gas, based on the kinetic molecular theory?
(1) There are attractive forces between the particles.
(2) The particles move in circular paths.
(3) The collisions between the particles reduce the total energy of the gas.
(4) The volume of the gas particles is negligible compared with the total volume of the gas
Solution: Kinetic molecular theory has the following statements which need to be memorized:
Gas particles have negligible volume.
The gas particles are in continuous random motion and move in straight lines.
No forces of attraction or repulsion are considered to exist between the particles.
Collisions of gas particles may transfer energy from one particle to another, but the total kinetic energy remains the same.
Answer: 4
15 Which statement describes a reaction at equilibrium?
(1) The mass of the products must equal the mass of the reactants.
(2) The entropy of the reactants must equal the entropy of the products.
(3) The rate of formation of the products must equal the rate of formation of the reactants.
(4) The number of moles of the reactants must equal the number of moles of the products.
Solution: At equilibrium the rates of forward and reverse reactions are equal.
Answer:3
16 Entropy is a measure of (1) accuracy (2) precision (3) the disorder of a system (4) the attraction of a nucleus for an electron
Solution: Entropy measures disorder of a system.
Answer: 3
17 Systems in nature tend to undergo changes toward (1) lower energy and less randomness (2) higher energy and less randomness (3) lower energy and greater randomness
(4) higher energy and greater randomness
Solution: Systems in nature tend to undergo changes toward lower energy and higher disorder
Answer: 3
44 Given the potential energy diagram representing a reaction:
Which numbered interval represents the heat of reaction? (1) 1
(2) 2 (3) 3
(4) 4
Solution: The heat of reaction is represented by the difference in the energy of reactants and products. 1 is the energy of reactants, 4 is the energy or products and 3 is the activation energy for the reverse reaction.
Answer: 2
August 2019
13 Given the equation representing a reaction: H + H → H2 What occurs during this reaction? (1) A bond is broken and energy is absorbed.
(2) A bond is broken and energy is released.
(3) A bond is formed and energy is absorbed.
(4) A bond is formed and energy is released.
Solution: When bond is formed energy is released. In the equation above two hydrogen atoms are coming together and forming a bond.
Answer: 4
18 According to the kinetic molecular theory, which statement describes the particles in a sample of an ideal gas?
(1) The particles are constantly moving in circular paths.
(2) The particles collide, decreasing the total energy of the system.
(3) The particles have attractive forces between them.
(4)The particles are considered to have negligible volume.
Solution: Kinetic molecular theory has the following statements which need to be memorized:
The gas particles are in continuous random motion and move in straight lines.
No forces of attraction or repulsion are considered to exist between the particles.
Collisions of gas particles may transfer energy from one particle to another, but the total kinetic energy remains the same.
Answer: 4
20 For a chemical system at equilibrium, the concentrations of both the reactants and the products must
(1) decrease
(2) increase (3) be constant
(4) be equal
Solution: At equilibrium the rates of forward and reverse reactions are equal and the concentrations of reactants and products stay constant.
Answer:3
21 In terms of disorder and energy, systems in nature have a tendency to undergo changes toward (1) less disorder and lower energy (2) less disorder and higher energy (3) greater disorder and lower energy
(4) greater disorder and higher energy
Solution: Systems in nature tend to undergo changes toward lower energy and higher disorder
Answer:3
41 Hydrochloric acid reacts faster with powdered zinc than with an equal mass of zinc strips because the greater surface area of the powdered zinc
(1) decreases the frequency of particle collisions
(2) decreases the activation energy of the reaction
(3) increases the frequency of particle collisions
(4) increases the activation energy of the reaction
Solution: Rate increases with increased surface area because it allowed for increased frequency of collisions of particles.
Answer: 3
42
Given the equation representing a system at equilibrium in a sealed, rigid container: 2HI(g) ⇌ H2(g) + I2(g) + energy
Increasing the temperature of the system causes the concentration of (1) HI to increase (2) H2 to increase (3) HI to remain constant
(4) H2 to remain constant
Solution: Notice that energy is on the right side (product side). Increasing temperature, means increasing energy. Having too much energy will shift equilibrium to the opposite side of where we see energy. In this case, equilibrium will shift to the left. This will increase the concentration of HI.
Answer: 1
43 Based on Table I, which equation represents a reaction with the greatest difference between the potential energy of the products and the potential energy of the reactants? (1) 4Al(s) + 3O2(g) → 2Al2O3(s) (2) 2H2(g) + O2(g) → 2H2O(l) (3) C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(l)
(4) C6H12O6(s) + 6O2(g) → 6CO2(g) + 6H2O(l)
Solution: ΔH is the difference between the potential energy of the products and the potential energy of the reactants. We can find each equation with the corresponding ΔH on Table I in the Reference Table. ΔH for choice 1 is –3351kJ , ΔH for 2 is–571.6kJ , ΔH for 3 is–2219.2kJ , ΔH for 4 is –2804 kJ
Now all we need to do is to see which one has the greatest absolute value of ΔH.
Answer: 1
44 Which phase change results in an increase in entropy? (1) I2(g) → I2(s)
(2) CH4(g) → CH4(l)
(3) Br2(l) → Br2(g)
(4) H2O(l) → H2O(s)
Solution: Entropy (disorder) increases as we go from solid to liquid to gas. Gas is the most disordered and liquid is the least disordered.
Answer: 3
June 2019
17 During which two processes does a substance release energy? (1) freezing and condensation (2) freezing and melting (3) evaporation and condensation
(4) evaporation and melting
Solution: Going from solid to liquid to gas, energy has to be absorbed. When gas turns into liquid and liquid turns into solid, energy is released. Freezing is going from liquid to solid and condensation is going from gas to liquid.
Answer: choice 1
18 Based on Table I, which compound dissolves in water by an exothermic process? (1) NaCl
(2) NaOH
(3) NH4Cl
(4) NH4NO3
Solution: Table I shows ΔH value for different reactions. If ΔH sign is positive that means reaction is endothermic. If ΔH sign is negative, that means reaction is exothermic. NaOH(s) in water reaction has a negative ΔH, which means it is exothermic.
Answer: Choice 2
21 Which value is defined as the difference between the potential energy of the products and the potential energy of the reactants during a chemical change? (1) heat of fusion (2) heat of reaction (3) heat of deposition
(4) heat of vaporization
Solution: Heat of reaction is the difference between the potential energy of the products and the potential energy of the reactants during a chemical change
Answer: Choice 2
22 The effect of a catalyst on a chemical reaction is to provide a new reaction pathway that results in a different (1) potential energy of the products
(2) heat of reaction (3) potential energy of the reactants
(4) activation energy
Solution: A catalyst is a substance that speeds up the reaction by lowering the activation energy.
Answer: Choice 4
23 Chemical systems in nature tend to undergo changes toward (1) lower energy and lower entropy
(2) lower energy and higher entropy
(3) higher energy and lower entropy
(4) higher energy and higher entropy
Solution: Chemical systems in nature tend to undergo changes toward higher entropy and lower energy.
Answer: Choice 2
42 Which sample of HCl(aq) reacts at the fastest rate with a 1.0-gram sample of iron filings? (1) 10. mL of 1 M HCl(aq) at 10.°C
(2) 10. mL of 1 M HCl(aq) at 25°C
(3) 10. mL of 3 M HCl(aq) at 10.°C
(4) 10. mL of 3 M HCl(aq) at 25°C
Solution: The higher the reactant concentration and the higher the temperature, the faster the rate of reaction will be.
Answer: Choice 4
43 Given the equation representing a system at equilibrium: N2O4(g) ⇌ 2NO2(g) Which statement describes the concentration of
the two gases in this system?
(1) The concentration of N2O4(g) must be less than the concentration of NO2(g).
(2) The concentration of N2O4(g) must be greater than the concentration of NO2(g).
(3) The concentration of N2O4(g) and the concentration of NO2(g) must be equal.
(4) The concentration of N2O4(g) and the concentration of NO2(g) must be constant.
Solution: At equilibrium the concentration of the reactants and products must be constant.
Answer: Choice 4
44 Given the equation representing a system at equilibrium: PCl5(g) + energy ⇌ PCl3(g) + Cl2(g) Which change will cause the equilibrium to shift to the right? (1) adding a catalyst (2) adding more PCl3(g) (3) increasing the pressure (4) increasing the temperature
Solution: Adding a catalyst does shift the equibrium. It just increases the rate of the reaction. Adding more PCl3 will cause shift to the left to get rid of PCl3. Increasing pressure means there is too much gas and we shift to the side with the least moles of gas, which is left. Increasing temperature will shift the equilibrium to the right since energy is on the left and we will want to go to the opposite side to lower it.
Answer: choice 4
January 2019
12 Which equation represents energy being absorbed as a bond is broken? (1) H+ H→H2 +energy
(2) H + H + energy→H2
(3) H2 →H+H+energy
(4) H2 +energy→H+H
Solution: If energy is absorbed, it should be on the reactant side, eliminating choices 1 and 3. In choice 1 we see two hydrogen atoms coming together to form a bond. In choice 4, we see a bond being broken.
Answer: 4
16 Which form of energy is transferred when an ice cube at 0°C is placed in a beaker of water at 50°C? (1) chemical
(2) electrical (3) nuclear
(4) thermal
Solution: Heat is transferred from a hotter object to a cooler one. This is thermal energy.
Answer: 4
17 The average kinetic energy of the particles in a sample of matter is expressed as (1) density (2) volume
(3) pressure
(4) temperature
Solution: Temperature is the measure of the average kinetic energy of the particles
Answer:4
19 Given the equation: I2(s) → I2(g) Which phrase describes this change? (1) endothermic chemical change
(2) endothermic physical change
(3) exothermic chemical change
(4) exothermic physical change
Solution: Since the formula does not change, this is a physical change. Going from solid to liquid requires heat (think heating ice to melt it). When heat is absorbed, this is called endothermic.
Answer: 2
20 Which term identifies a factor that will shift a chemical equilibrium?
(1) atomic radius
(2) catalyst (3) decay mode
(4) temperature
Solution: Changes in temperature, concentration, volume and pressure can shift a chemical equibrium.
Answer: 4
21 According to which theory or law is a chemical reaction most likely to occur when two particles with the proper energy and orientation interact with each other? (1) atomic theory (2) collision theory (3) combined gas law (4) law of conservation of matter
Solution: Collision theory states that a chemical reaction most likely to occur when two particles with the proper energy and orientation interact with each other
Answer:2
22 Addition of a catalyst can speed up a reaction by providing an alternate reaction pathway that has a (1) lower activation energy
(2) higher activation energy
(3) lower heat of reaction
(4) higher heat of reaction
Solution: Addition of a catalyst can speed up a reaction by providing an alternate reaction pathway that has a lower activation energy.
Answer:1
42 During which phase change does the entropy of a sample of H2O increase? (1) H2O(g) → H2O(l)
(2) H2O(g) → H2O(s)
(3) H2O(l) → H2O(g)
(4) H2O(l) → H2O(s)
Solution: Gases are most disordered (highest entropy) and solids are least disordered (lowest entropy).
Answer: 3
August 2018
12 Which statement describes the energy changes that occur as bonds are broken and formed during a chemical reaction?
(1) Energy is absorbed when bonds are both broken and formed.
(2) Energy is released when bonds are both broken and formed.
(3) Energy is absorbed when bonds are broken, and energy is released when bonds are formed.
(4) Energy is released when bonds are broken, and energy is absorbed when bonds are formed.
Solution: When bonds are formed energy is released and when bonds are broken energy is absorbed.
Answer:3
17 A cube of iron at 20.°C is placed in contact with a cube of copper at 60.°C. Which statement describes the initial flow of heat between the cubes?
(1) Heat flows from the copper cube to the iron cube.
(2) Heat flows from the iron cube to the copper cube.
(3) Heat flows in both directions between the cubes.
(4) Heat does not flow between the cubes.
Solution: Heat always flows from the hotter to the cooler object.
Answer: 1
20 In terms of entropy and energy, systems in nature tend to undergo changes toward (1) lower entropy and lower energy
(2) lower entropy and higher energy
(3) higher entropy and lower energy
(4) higher entropy and higher energy
Solution: Systems in nature tend to undergo changes toward higher entropy and lower energy.
Answer:3
24 For a reaction system at equilibrium, LeChatelier’s principle can be used to predict the (1) activation energy for the system
(2) type of bonds in the reactants (3) effect of a stress on the system
(4) polarity of the product molecules
Solution: LeChatelier’s principle can be used to predict the effect of a stress on the system. It states that the system will shift in a way to reestablish the equilibrium.
Answer: 3
43 The equation below represents a reaction between two molecules, X2 and Z2. These molecules form an “activated complex,” which then forms molecules of the product.
Which diagram represents the most likely orientation of X2 and Z2 when the molecules collide with proper energy, producing an activated complex?
Solution: We can look at the activated complex to see which orientation will be most likely to produce the products.
Answer: 2
January 2018
11 Given the equation representing a reaction: O + O → O2 Which statement describes the changes that occur as the oxygen molecule is produced? (1) Energy is absorbed as bonds are broken.
(2) Energy is absorbed as bonds are formed.
(3) Energy is released as bonds are broken.
(4) Energy is released as bonds are formed.
Solution: We can see two oxygen atoms coming together to form O2. When a bond is formed, energy is released.
Answer: 4
17 A chemical reaction is most likely to occur when the colliding particles have the proper (1) energy and orientation
(2) solubility and density
(3) ionic radii and mass
(4) atomic radii and volume
Solution: Particles must have proper orientation and enough energy in order to collide successfully and form products.
Answer:1
18 The energy absorbed and the energy released during a chemical reaction are best represented by a (1) cooling curve (2) heating curve (3) kinetic energy diagram
(4) potential energy diagram
Solution: Potential energy diagram shows the energy of reactants and products and whether the reaction is exothermic or endothermic.
Answer:4
19 A catalyst increases the rate of a chemical reaction by
(1) providing an alternate reaction pathway
(2) providing the required heat of reaction
(3) increasing the potential energy of the products
(4) increasing the activation energy of the reaction
Solution: A catalyst increases the rate of a chemical reaction by decreasing the activation energy of the reaction by providing an alternate reaction pathway.
Answer:1
40 Given samples of water:
Sample 1: 100. grams of water at 10.°C Sample 2: 100. grams of water at 20.°C
Compared to sample 1, sample 2 contains (1) molecules with a lower average kinetic energy
(2) molecules with a lower average velocity (3) less heat energy (4) more heat energy
Solution: Temperature is the measure of the average kinetic energy. Sample 2 is higher temperature and would have a higher kinetic energy. Since it is higher temperature, it would have a higher heat energy.
Answer:4
44 What is the net amount of heat released when two moles of C2H6(g) are formed from its elements at 101.3 kPa and 298 K? (1) 42.0 kJ
(2) 84.0 kJ
(3) 126.0 kJ
(4) 168.0 kJ
Solution: We need to take a look at Table I on the Reference Table for the net amount of heat released. We can find the equation where C2H6(g) is the product. 2C(s) + 3H2(g) -->C2H6(g) ΔH = –84.0 The question asks for 2 moles of C2H6(g) and we see that the equation only produces 1 mole of C2H6(g) (the coefficient is 1 in the equation). Therefore we must multiply ΔH by 2, 84.0*2 = 168.0 kJ
Answer: 4
June 2018
19 A chemical reaction occurs when reactant particles
(1) are separated by great distances
(2) have no attractive forces between them
(3) collide with proper energy and proper orientation
(4) convert chemical energy into nuclear energy
Solution: A chemical reaction occurs when reactant particlesc ollide with proper energy and proper orientation.
Answer: 3
20 Systems in nature tend to undergo changes toward (1) lower energy and lower entropy
(2) lower energy and higher entropy
(3) higher energy and lower entropy
(4) higher energy and higher entropy
Solution: Systems in nature tend to undergo changes toward lower energy and more disorder (higher entropy)
Answer: 2
44 Based on Table I, what is the ΔH value for the production of 1.00 mole of NO2(g) from its elements at 101.3 kPa and 298 K? (1) +33.2 kJ
(2) -33.2 kJ
(3) +132.8 kJ
(4) -132.8 kJ
Solution: We need to take a look at Table I on the Reference Table for the net amount of heat released. We can find the equation where NO2(g) is the product.
N2(g) + 2O2(g) -> 2NO2(g) ΔH = +66.4
In the equation, the coefficient in front of NO2 is 2 signifying 2 moles being produced. We are asked for the production of 1 mole. We need to half the ΔH value.
Answer: 1
June 2017
15 The average kinetic energy of water molecules decreases when (1) H2O(l) at 337 K changes to H2O(l) at 300. K
(2) H2O(l) at 373 K changes to H2O(g) at 373 K
(3) H2O(s) at 200. K changes to H2O(s) at 237 K
(4) H2O(s) at 273 K changes to H2O(l) at 273 K
Solution: Temperature is the measure of the average kinetic energy. Therefore, going from higher to lower temperature means a decrease in the average kinetic energy.
Answer: 1
22 When a reversible reaction is at equilibrium, the concentration of products and the concentration of reactants must be
(1) decreasing
(2) increasing (3) constant
(4) equal
Solution: At equilibrium, the concentration of products and the concentration of reactants must be constant
Answer: 3
23 In chemical reactions, the difference between the potential energy of the products and the potential energy of the reactants is equal to the (1) activation energy
(2) ionization energy
(3) heat of reaction (4) heat of vaporization
Solution: The difference between the potential energy of the products and the potential energy of the reactants is equal to the heat of reaction
Answer: 3
24 What occurs when a catalyst is added to a chemical reaction?
(1) an alternate reaction pathway with a lower activation energy
(2) an alternate reaction pathway with a higher activation energy
(3) the same reaction pathway with a lower activation energy
(4) the same reaction pathway with a higher activation energy
Solution: A catalyst lowers the activation energy by providing a new pathway for the reaction.
Answer: 1
42 Given the equation representing a chemical reaction at equilibrium in a sealed, rigid container:
H2(g) + I2(g) + energy ⇌2HI(g)
When the concentration of H2(g) is increased by adding more hydrogen gas to the container at constant temperature, the equilibrium shifts
(1) to the right, and the concentration of HI(g) decreases
(2) to the right, and the concentration of HI(g) increases
(3) to the left, and the concentration of HI(g) decreases
(4) to the left, and the concentration of HI(g) increases
Solution: When more hydrogen is added, that means we have too much hydrogen and need to shift to the opposite side to decrease it. The equilibrium will shift to the right, increasing the concentration of HI
Answer:2
43 Which diagram represents the potential energy changes during an exothermic reaction?
Solution: In an exothermic reaction, energy is released. The dingy of the products must be lower then the energy of the reactants.
Answer:4
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