A Level Chemistry OCR Practice Exam

Which of the following best describes an enthalpy profile diagram?

1. A diagram comparing temperature changes over time

2. A diagram that illustrates enthalpy changes during a phase change

3. A diagram to compare the enthalpy of reactants and products

4. A diagram showing the molecular structure of organic compounds

The correct answer is: A diagram to compare the enthalpy of reactants and products

An enthalpy profile diagram is specifically designed to illustrate the enthalpy changes associated with a chemical reaction, typically displaying the enthalpy of reactants compared to that of products. This diagram demonstrates the potential energy of the reactants and products and highlights the energy changes that occur during the course of the reaction, including the activation energy barrier. The correct answer captures the essence of how energy is transformed in a reaction, which is fundamental to understanding reaction dynamics and thermodynamics. Such diagrams enable chemists to visualize the energy relationships that define whether a reaction is exothermic or endothermic. Other options, while relating to energy or temperature in various ways, do not encapsulate the primary purpose of an enthalpy profile diagram. For instance, comparing temperature changes over time pertains more to kinetic studies than thermodynamic enthalpy. Illustrating enthalpy changes during a phase change focuses on the changes in state rather than the energy transfer in a chemical reaction context. Lastly, molecular structure diagrams are concerned with the arrangement of atoms rather than the energy aspects of reactants and products in a reaction. Thus, the correct answer effectively represents the function of an enthalpy profile diagram in chemical thermodynamics.