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During all chemical reactions, charge, mass and energy are

Regents Chemistry Exam June 2019

Questions 11-20

11 During all chemical reactions, charge, mass and energy are

(1) condensed

(2) conserved (3) decayed (4) decomposed

Solution: This is something that we need to remember. Charge, mass and energy are conserved during all chemical reactions.

Answer: Choice 2

12 The degree of polarity of a covalent bond between two atoms is determined by calculating the difference in their

(1) atomic radii

(2) melting points (3) electronegativities

(4) ionization energies

Solution: The difference in electronegativity determines how polar a covalent bond is. The higher the difference, the more polar the bond.

Answer: Choice 3

13 Which substance can not be broken down by a chemical change?

(1) ammonia

(2) magnesium (3) methane

(4) water

Solution: Elements can not be broken down by a chemical change. Out of all the choices, magnesium is the only element.

Answer: Choice 2

14 Which statement describes the components of a mixture?

(1) Each component gains new properties. (2) Each component loses its original properties.

(3) The proportions of components can vary. (4) The proportions of components cannot vary.

Solution: In a mixture, the proportion of components can vary. For example, salt and water, could be 50% salt and 50% water or 70% salt and 30% water etc

Answer: Choice 3

15 Table sugar can be separated from a mixture of table sugar and sand at STP by adding

(1) sand, stirring, and distilling at 100.°C

(2) sand, stirring, and filtering (3) water, stirring, and distilling at 100.°C

(4) water, stirring, and filtering

Solution: Sugar dissolves in water while sand does now. We can separate sugar and sand by adding water, stirring and filtering. During filtering, sand will stay on the filter while sugar dissolved in water will pass through.

Answer: Choice 4

16 Which statement describes the particles of an ideal gas, based on the kinetic molecular theory?

(1) The volume of the particles is considered negligible.

(2) The force of attraction between the particles is strong.

(3) The particles are closely packed in a regular, repeating pattern.

(4) The particles are separated by small distances, relative to their size.

Solution: One of the statements of kinetic molecular theory is that the volume of particles of ideal gas is negligible ( we assume they have no volume).

Answer: choice 1

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

19 At STP, which property of a molecular substance is determined by the arrangement of its molecules? (1) half-life (2) molar mass (3) physical state (4) percent composition

Solution: The physical state is a property of a molecular substance is determined by the arrangement of its molecules. For example, when particles are arranged closely together, the phase is solid.

Answer: Choice 3

20 Equilibrium can be reached by (1) physical changes, only (2) nuclear changes, only (3) both physical changes and chemical changes

(4) both nuclear changes and chemical changes

Solution: There can be physical equilibrium (between different physical states such as solid turning into liquid and back) as well as chemical equilibrium (where a reaction happens).

Answer: Choice 3



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