THERMOCHEMISTRYChapter 6 Review

Learn definitions that describe the systems studied in thermochemistry Explain what is meant by a system and its surroundings. Explain what is meant by a state function. Be able to calculate the change in energy of a system as well at the work of the system. State the 1st Law of Thermodynamics. Apply the 1st Law of Thermodynamics quantitatively. Understand the meaning of the terms exothermic and endothermic. Describe enthalpy and balance thermochemical equations. Calculate enthalpy changes in physical and chemical processes. Use Hess's Law to calculate heat of reaction for multi-step reactions. Write out heat of formation equations and use heat of formation to calculate heat of reaction.

Review Questions1. Calculate the ΔE for each of the following cases:

a. 51 kJ of absorbed heat and 15 kJ of work done by the system.

b. 65 kJ of released heat and 20 kJ of work done by the system.

2. A balloon filled with 25.0mol of neon has a volume of 100.0L at 0.0°C and it expands to a volume of 255.0L with a new temperature of 38.0°C at a constant pressure, 1.00 atm. Calculate q, w, and ΔE for the neon in the balloon. The molar heat capacity for neon is 20.8 J/mol°C.

3. The value of ΔH° for the reaction below is -482 kJ. Calculate the heat in kJ released to the surroundings when 23.0g of HCl is formed. CH4(g) + 3Cl2(g) → CHCl3(l) + 3HCl(g).

4. Consider the following equations:

(1) CH3OH(l) + O2(g) → HCHO2(l) + H2O(l) ΔH° = -411 kJ(2) CO(g) + 2H2(g) → CH3OH(l) ΔH° = -128 kJ(3) HCHO2(l) → CO(g) + H2O(l) ΔH° = -33 kJ

Suppose equation (1) is reversed and divided by 2, equations (2) and (3) are multiplied by ½ and then the three adjusted equations are added. What is the net reaction and what is the value of ΔH° for the net reaction?

5. Using the Hf given below, calculate the Hcombustion for propane, C3H8.Hf (kJ/mol)

H2O(l) -286CO2(g) -394C3H8(g) -104

6. Which equation represents the heat of formation, Hf, for MgCl2?a. Mg2+

(aq) + 2 Cl-(aq) MgCl2(s)

b. Mg(s) + 2 Cl(g) MgCl2(s)

c. MgCl2(s) Mg2+(aq) + 2 Cl–(aq)

d. Mg(s) + Cl2(g) MgCl2(s)

7. A gas at 20 atm pressure with a volume of 2.0 Liters expands against a 5 atm pressure to a volume of 8.0 Liters. How much work is done by the gas?

a. 30 Latm c. 8 Latmb. 18 Latm d. 5 Latm

8. Take a toy balloon. Quickly stretch the balloon and press it against your lower lip. What is the H for the reaction: unstretched stretcheda. + b. 0 c. d. impossible to tell

9. Which of the following is NOT a state function?a. pressure c. temperatureb. volume d. none of these

10. The bond enthalpy of the Br-Cl bond is equal to the ∆H° for the reaction BrCl(g) → Br(g) + Cl(g). Using the following data, find the bond enthalpy of the Br-Cl bond.Br2(l) → Br2(g) ∆H° = 30.91 kJ/molBr2(g) → 2Br(g) ∆H° = 192.9 kJ/molCl2(g) → 2Cl(g) ∆H° = 243.4 kJ/molBr2(l) + Cl2(g) → 2BrCl(g) ∆H° = 29.2 kJ/mol a. 407.0 kJ/mol d. 219.0 kJ/molb. 14.6 kJ/mol e. 203.5 kJ/molc. 438.0 kJ/mol

11. A gas is allowed to expand, at a constant temperature, from a volume of 1.0L to 10.1L against an external pressure of 0.50atm. If the gas absorbs 250J of heat from its surroundings, what are the values of q, w, and ∆E?

q w ∆E Row 1 250J -460J -210JRow 2 -250J -460J -710JRow 3 250J 460J 710JRow 4 -250J 460J 210JRow 5 250J 4.55J 245J

a. Row 3 d. Row 2b. Row 1 e. Row 5c. Row 4

12. Calculate the amount of work done against an atmospheric pressure of 1.00atm when 500.0g zinc dissolves in excess acid at 30.0°C Zn(s) + 2H+

(aq) → Zn+2(aq) + H2(g)

a. w = +24.9kJ d. w = -2.52kJb. w = -19.3kJ e. w = +22.4kJc. w = 0

13. Given the following data, calculate the ∆H for the reaction: 2N2(g) + 6H2O(g) → 3O2(g) + 4NH3(g). On the basis of the enthalpy change that you calculate, is this a useful reaction for the synthesis of ammonia?

NH3(g) → 12N2(g) +

32 H2(g) ∆H = 46 kJ

2H2(g) + O2(g) → 2H2O(g) ∆H = -484 kJ

14. Using the table of standard enthalpies in your text, calculate the standard enthalpy change at 298K for the following reactions:a. CH4(g) + 4CuO(s) → CO2(g) + 2H2O(g) + 4Cu(s)

b. CaCO3(s) → CaO(s) + CO2(g)