Energy in Chemical Reactions

Study Questions

1.         What is energy?

2.         What is heat?

3.         Where is energy stored in a chemical compound?

4.         State the law of conservation of energy.

5.         What is an endothermic reaction?

6.         What is an exothermic reaction?

7.         How do you recognize an exothermic reaction?

8.         What is the most noticeable property of an endothermic reaction?

9.         Why is added energy needed to sustain an endothermic reaction?

10.        What is the difference between a positive and a negative DH n terms of energy and the kind of reaction involved?

11.        What is activation energy?

12.       How do catalysts lower activation energy?

13.       An endothermic reaction absorbs energy. Why don’t the products become hotter?

14        How does energy level drive chemical reactions?

15.       Why is outside energy needed to start most exothermic reactions but not to sustain them?

16.       What would cause a reaction to go where the products had a higher energy level than the reactants?

17.       Analyze an energy graph for a reaction.

18       What is entropy?

19.       Is entropy conserved? Explain your choice.

20.       In terms of order and disorder, in what direction do naturally occurring processes go?

21.       What are five types of disorder affecting chemical reactions?

22.       What is the change from a solid to a gas considered a change in entropy?

23.       Are reactions that occur spontaneously at room temperature exothermic or endo thermic? Explain.

24.       Describe the energy changes that occur when a match lights.

25.       DH for a reaction is negative. Compare the energy of the products and reactants. Is the reaction endothermic or exothermic?

26.       The first state in fermentation is: C₆H₁₂O6_(aq) –> 2C₂H₅OH_(aq) + 2CO_2(g) + Q. Does entropy increase or decrease? Relate the energy and entropy changes to the reactions spontaneity.

27.       What is the purpose of calorimetry?

28.       What is specific heat?

29.       How is a calorimeter used to measure heat?

30.       What is the formula for Q?

31.       What is a kilocalorie?

32.       What is the relationship between kilocalories and joules?

33.       What three variables determine the amount of heat produced or used in a reaction?

34.       A tablespoon of butter has 100 Calories of energy. How many joules are present?

35.       How do food scientists determine the amount of energy in a food?

36.       84g of beef burned in a calorimeter produce 241 Calories of energy. How much energy is

produced when it is digested by a teenager?

37.       Explain the energy benefits of recyling?

38.       Why must entropy be considered in our energy use decisions?

39.       What is the relationship between chemical energy and the electricity we use in our homes?

40       Why is it impossible to convert 100% of the energy stored in fossil fuels to electricity?

41.       The specific heat of aluminum is 0.902J/gºC. The specific heat of copper is 0.389J/gºC. If the same amount of heat is applied to a kg of each metal, which metal will increase more in temperature? Explain.

42.       What is the overall reaction for photsynthesis?

43.       What is the purpose of photosynthesis?

44.       What is the purpose of respiration?

45.       Describe the light reactions of photosynthesis.

46.       What particle carries the energy between molecules in the light reactions?

47.       What molecules are used to store energy in the light reactions?

48.       What are the products of the light reactions?

49.       What is the purpose of water in the light reactions?

50.       The Calvin cycle happens without light. What provided the energy to power the dark reactions?

51.       What converts PGA to PGAL?

52.       How many C atoms are added for each loop of the Calvin cycle?

53.       How many loops of the Calvin cycle are required to produce 1 glucose molecule?

54.       Photosynthesis results in lower entropy in the products. How can this be reconciled with the fact that entropy tends to increase?

55.       Plants appear green because leaves reflect green and yellow light. What happens to the energy in the wavelengths of light that are not reflected?

56.       What would be the effect on Earth’s atmosphere if plants were unable to photosynthesize?

57.        Account for the fact that there is an energy difference in the following reactions

            a.         CH_4(g) + 2O_2(g) –> CO_2(g) + 2H₂O_(l) DH = -802kJ

            b.         CH_4(g) + 2O_2(g) –> CO_2(g) + 2H₂O_(g) DH = -890kJ

58.       The specific heat of Pb is -.128K/gºC. How much heat is required to raise the temperature of 10.0g of Pb from 20 ºC to 30ºC?

59.      The heats of formation of the hydrogen halides are listed below. Using this information

predict which compound is most stable and which is least stable. Explain your choices.