June 2023 NY Regents Chemistry Exam
44 A potential energy diagram for a chemical reaction is given below. Each interval on the potential energy axis represents 100. kilojoules of potential energy.
What can be concluded from the diagram? (1) The reaction is endothermic, and the heat of reaction is -200. kJ. (2) The reaction is endothermic, and the heat of reaction is +200. kJ. (3) The reaction is exothermic, and the heat of reaction is -200. kJ. (4) The reaction is exothermic, and the heat of reaction is +200. kJ.
Solution: The heat of the reaction is the difference between the energy of products (horizontal line on the right side) and reactants (horizontal line on the left side). Each interval represents 100kJ according to the given. There are two intervals in between the two horizontal lines, representing 100kJ*2 = 200KJ.
The line for products is higher than the line for reactants which means energy is absorbed and the reaction is endothermic. For an endothermic reaction, the sign for heat of reaction will be positive.
Answer: 2
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