Reaction Energy Profile - AP Chemistry

1. State the effect of concentration increase on reaction rate.

   Increases reaction rate. More reactant molecules increase collision frequency and reaction rate.

2. What is the unit of activation energy?

   Typically joules per mole (J/mol). Energy per mole represents the barrier height for molecular-scale reactions.

3. Identify the term for the highest energy point in a reaction energy profile.

   Transition state. This point represents the activated complex at maximum potential energy.

4. Identify the component of the reaction energy profile that changes with a catalyst.

   The activation energy ($E_a$). Catalysts only affect activation energy, not the overall enthalpy change.

5. What is the definition of activation energy in a chemical reaction?

   The minimum energy required to initiate a chemical reaction. This energy barrier must be overcome for reactant bonds to break and form products.

6. Which part of a reaction energy profile represents the activated complex?

   The peak of the energy curve. The transition state occurs at maximum energy where bonds are breaking and forming.

7. Find and correct: 'Catalysts increase the enthalpy change of a reaction.'

   Correct: 'Catalysts do not change enthalpy.'. Catalysts affect kinetics but leave thermodynamic properties unchanged.

8. Find and correct: 'The transition state has the lowest energy in a reaction.'

   Correct: 'highest energy.'. The transition state represents the maximum energy point during reaction.

9. State the definition of the activated complex in a reaction.

   A transitional structure formed during a reaction. This unstable intermediate exists at the energy maximum during bond reorganization.

10. Find and correct: 'Exothermic reactions have $\Delta H > 0$.'

    Correct: '$\Delta H < 0$'. Exothermic reactions release energy, requiring negative enthalpy change values.

11. Which option shows a reaction with a negative $\Delta H$?

    An exothermic reaction. Negative $\Delta H$ means products are lower in energy, releasing heat.

12. What does a lower peak in the presence of a catalyst indicate?

    Reduced activation energy. Catalysts create alternative pathways requiring less energy to reach products.

13. What is the typical unit for reaction rate?

    Moles per liter per second (M/s). Rate measures concentration change per unit time in chemical reactions.

14. Identify the main effect of temperature increase on reaction rate.

    Increases reaction rate. Higher temperatures provide more kinetic energy to overcome activation barriers.

15. What does a reaction energy profile illustrate?

    Energy changes during a reaction. These diagrams show energy transformations from reactants through products.

16. State the definition of the activated complex in a reaction.

    A transitional structure formed during a reaction. This unstable intermediate exists at the energy maximum during bond reorganization.

17. State the role of temperature in reaction energy profile analysis.

    Affects activation energy. Higher temperatures increase molecular kinetic energy, affecting reaction barriers.

18. What is the effect of particle size decrease on reaction rate?

    Increases reaction rate. Smaller particles have greater surface area, increasing collision frequency.

19. What is the effect of pressure increase on reaction rate for gases?

    Increases reaction rate. Higher pressure increases gas molecule density and collision frequency.

20. State the term for the energy difference between reactants and the activated complex.

    Activation energy ($E_a$). This energy difference determines how fast the reaction proceeds.

21. Identify the term for reactions that release energy to the surroundings.

    Exothermic reactions. These reactions release energy, making products lower in energy than reactants.

22. Which option shows a reaction with energy absorbed from the surroundings?

    An endothermic reaction. Energy absorption occurs when products form at higher energy than reactants.

23. Which direction of enthalpy change (positive/negative) indicates an endothermic reaction?

    Positive $\Delta H$ indicates endothermic. Energy flows from surroundings to the system when $\Delta H > 0$.

24. Identify the reaction type if products are higher in energy than reactants.

    Endothermic reaction. Higher product energy means the reaction absorbs heat from surroundings.

25. Which option shows a reaction with energy released as heat?

    An exothermic reaction. Heat release occurs when products form at lower energy than reactants.

26. Identify the term for reactions that release energy to the surroundings.

    Exothermic reactions. These reactions release energy, making products lower in energy than reactants.

27. What is the significance of the peak in a reaction energy profile?

    It represents the transition state. The highest point corresponds to the unstable activated complex formation.

28. What is the effect of a catalyst on activation energy?

    Catalysts lower the activation energy. They provide alternative pathways with lower energy barriers for reactions.

29. Which factor does not change the enthalpy change of a reaction?

    A catalyst. Catalysts affect reaction rate but not the thermodynamic energy change.

30. Which option shows a reaction with a positive $\Delta H$?

    An endothermic reaction. Positive $\Delta H$ means products are higher in energy, absorbing heat.

31. What is the formula to calculate the enthalpy change, $\Delta H$?

    $\Delta H = \text{Energy of products} - \text{Energy of reactants}$. This formula calculates the net energy change from reactants to products.

32. Find and correct: 'A catalyst increases the activation energy.'

    Correct: 'Catalyst lowers activation energy.'. Catalysts provide alternative pathways with lower activation energy barriers.

33. What is the significance of the peak in a reaction energy profile?

    It represents the transition state. The highest point corresponds to the unstable activated complex formation.

34. Which option correctly describes the role of a catalyst in a reaction?

    A catalyst speeds up the reaction. Catalysts increase reaction rates by lowering activation energy barriers.

35. What does the energy difference between reactants and products indicate?

    The enthalpy change ($\Delta H$) of the reaction. This represents the overall heat absorbed or released in the reaction.

36. Find and correct: 'In exothermic reactions, products have higher energy than reactants.'

    Correct: 'products have lower energy.'. Exothermic reactions release energy, so products must have lower energy.

37. Identify the reaction type if products are lower in energy than reactants.

    Exothermic reaction. Lower product energy means the reaction releases heat to surroundings.

38. What is the influence of a catalyst on reaction equilibrium?

    No change in equilibrium position. Catalysts speed reactions equally in both directions, maintaining equilibrium.

39. Identify the term for reactions that absorb energy from the surroundings.

    Endothermic reactions. These reactions require energy input, making products higher in energy than reactants.

40. What does the energy difference between reactants and products indicate?

    The enthalpy change ($\Delta H$) of the reaction. This represents the overall heat absorbed or released in the reaction.

41. Find and correct: 'Endothermic reactions have $\Delta H < 0$.'

    Correct: '$\Delta H > 0$'. Endothermic reactions absorb energy, requiring positive enthalpy change values.

42. Identify the variable for reaction rate in a chemical equation.

    The rate is typically denoted as $r$. Rate measures how fast reactants convert to products over time.

43. Which direction of enthalpy change (positive/negative) indicates an exothermic reaction?

    Negative $\Delta H$ indicates exothermic. Energy flows from the system to surroundings when $\Delta H < 0$.

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