Unit Review: Thermodynamics (2013)

DIRECTIONS: Answer the questions that follow. For questions that involve mathematics: show work, use units, use sig figs.

12.1, 12.4, and 12.8

1. Calculate the energy required (in joules) to heat 25.0 g of ethanol from 18.0C to 29.5C. The specific heat of ethanol is 2.44 J/g°C.

2. In lab, 4.4 grams of substance A went from 25°C to 46°C when 26 J of energy was transferred to it. What is the specific heat capacity of substance A?

3. The specific heat of a substance is 2.1 J/g°C. If 126 joules of heat are absorbed by 15g of the substance at 30°C, what will be the substance’s final temperature?

4. Below is data similar to the data you collected in lab. Find the specific heat of the unknown solid using the data.

Mass of the solid………………………………………………………………………………..52.8 g

Volume of water in the Styrofoam cup (for water 1g/1mL)……....65.1 mL

Starting temperature of water in Styrofoam cup……………………...29.2°C

Highest temperature of water in cup after the solid was it ..…33.7°C

Temperature of the boiling water (and solid)…....……………………...100.0°C

5. The British Isles (off the coast of Europe) are located at about the same latitude as Novia Scotia and Labrador in North America. The climate of the British Isles, however, is much warmer than that of Nova Scotia and Labrador. Explain this using principles of chemistry.

12.3

6. Define specific heat.

7. Note these specific heats: lead = 0.13 J/g°C; aluminum = 0.90 J/g°C;

iron = 0.449 J/g°C; gold = 0.129 J/g°C

  1. You have equal masses of each of the four substances at the same

temperature. If you put each of them into a separate calorimeters with 25.0 mL of water at 25°C, which would change the temperature of the water the least? Why?

  1. If you have equal masses of each of the four substances above at the same

temperature, which would hold the most heat? Or would they all hold the

same amount of heat? Why?

12.2

8. Write the Law of Conservation of Energy.

9. How did we make use of the Law of Conservation of Energy in this unit?

12.9 and 12.10

10. For each reaction that follows, (i) do the Lewis dot diagram and (ii) se the list of

bond energies AT THE END OF THIS REVIEW to calculate the change in

enthalpy (∆H) for the reactions below.

  1. CH4 + 2Cl2 + 2F2  CF2Cl2 + 2HF + 2HCl
  2. 2NCl3 + 3F2  2NF3 + 3Cl2

11. In terms of bond energies: (a) what makes a reaction exothermic? (b) what makes a

reaction endothermic? (Hint: see the next question)

12. When bonds are broken, energy is _____; when bonds form, energy is _____.

12.7

13. What are the five states of matter? Describe each.

14. With what two states of matter are you unlikely to have any personal experiences? Why?

12.11

15. What conditions of ∆H and ∆S would be necessary for a reaction to be spontaneous at any temperature?

16. If ∆H is 424 kJ and ∆S is 0.0551 kJ at -75.0°C, what is ∆G? Is the reaction spontaneous?

17. What do we mean when we say that a reaction is not spontaneous?

12.12

18. Draw a potential energy diagram using the information below and answer the questions that follow.

  1. potential energy of the reactants: 50
  2. potential energy of the products: 200
  3. potential energy of the transition state: 300

Questions

  1. What is the activation energy of the forward reaction_____
  2. What is the activation energy of the reverse reaction_____
  3. What is the change in enthalpy (∆H) _____
  4. Is the reaction exothermic or endothermic? _____