AP Chemistry Name :

Worksheet : Chapter 6 ; obj. 1-19-22Date :

A. Multiple choice – Calculators may be used.

1. You take 200. g of a solid at 30.0 ºC and let it melt in 400. g of water. The water temperature decreases from 85.1 ºC to 30.0 ºC. Calculate the heat of fusion(heat needed to melt)of this solid.

a. 125 J/g

b. 285 J/g

c. 461 J/g

d. 518 J/g

e. cannot without the heat capacity of the solid

2. Calculate the work associated with the compression of a gas from 121 L to 80. L at a constant pressure of 11 atm.

a. -450 L · atm

b. 450 L · atm

c. 3.7 L · atm

d. -3.7 L · atm

e. 120 L · atm

3. The total volume of hydrogen gas needed to fill the Hindenburg was 2.00 x 108 L at 1.00 atm and 25.0 ºC. How much energy was evolved when it burned? (assume 1 mol = 22.42L)

H2(g) + (1/2)O2(g)  H2O(l), ΔH = -286 kJ

a. 3.5 x 1011 kJ

b. 8.18 x 106 kJ

c. 2.86 x 104 kJ

d. 2.55 x 109 kJ

e. 5.72 x 1010 kJ

4. When 0.157 mol NH3 is reacted with excess HCl, 6.91 kJ of energy is released as heat. What is ΔH for this reaction per mole of NH3 consumed?

a. -22.7 J

b. -1.08 kJ

c. -44.0 kJ

d. +22.7 J

e. +44.0 kJ

5. Choose the correct equation for the standard enthalpy of formation .of CO(g), where ΔHŒ for CO = -110.5 kJ/mol (gr indicates graphite).

a. 2C(gr) + O2 (g)  2CO(g), ΔHº = -110.5 kJ

b. C(gr) + O(g)  CO(g), ΔHº = -110.5 kJ

c. C(gr) + (1/2)O2(g)  CO(g), ΔHº = -110.5 kJ

d. C(gr) + CO2 (g)  2CO(g), ΔHº = -110.5 kJ

e. CO(g)  C(gr) + O(g), ΔHº = -110.5 kJ

6. The specific heat of aluminum is 0.900 J/g·°C. How much heat is released when 1.2 kg of aluminum is cooled from 125 °C to 30. °C?

7. It takes 154.2 J to raise the temperature of 91.2 g of lead from 26.2 °C to 39.5 °C. Calculate the molar and specific heats of lead.

8. A 50.0 g sample of water at 88.8 °C is mixed with a 35.0 g sample of water at 17.5 °C. Calculate the final temperature of the mixture. (s = 4.18 J/g·°C, Tf is same for both solutions after mixing, heat lost = heat gained).

9. A 46.2 gram sample of a metal is heated to 105 °C and placed in a coffee cup calorimeter containing 200. grams of water at 22.0 °C. After the copper is placed in the water and the system reached equilibrium, the temperature of the water and metal is 24.2 °C. Calculate the specific heat of the metal.

10. In a coffee cup calorimeter, 200.0 ml of 1.0 M NaOH and 200.0 mL of 1.0 M HCl are mixed. Both solutions were originally at 22.0 °C. After the reaction, the final temperature is 28.7 °C. Assume all solutions have a density of 1.0 g/cm3 and a specific heat capacity of 4.18 J/g·°C, calculate the enthalpy change (in kJ/mol)for the neutralization reaction of HCl and NaOH. (Also assume no heat loss to the surroundings).

11. In a coffee cup calorimeter, 50.0 mL of 0.100 M AgNO3 is mixed with 50.0 mL of 0.100 M HCl to yield the following reaction : Ag+(aq) + Cl-(aq)  AgCl(s). The two solutions were originally at 22.60 °C, and the temperature rose to 23.40 °C after the reaction was complete. Calculate the heat of formation of AgCl from its ions in kJ/mol. Assume the total mass of the solution is 100.0 g and the specific heat of the solution is 4.18 J/g ·°C).

12. Camphor (C10H16O) has a heat of combustion of -5903.6 kJ/mol. When 0.1204 g of camphor is burned in a bomb calorimeter, the temperature increases by 2.28 °C. Calculate the heat capacity of this bomb calorimeter. (units are kJ/°C)

13. When a 2.000-gram sample of pure methanol, CH3OH, is burned 45.30 kilojoules of heat is released. Use the information in the table below to answer the questions that follow.

Substance / Standard Heat of Formation, Hâ; at 25C (kJ/mol)
C(graphite) / 0.00
CO2(g) / -393.5
H2(g) / 0.00
H2O(l) / -285.85
O2(g) / 0.00
CH3OH(l) / ?

(a)Write the balanced chemical reaction for the combustion of methanol.

(b) Calculate the molar heat of combustion of methanol in kilojoules per mole at 25C.

(c)Calculate the standard heat of formation, Hf, of methanol in kilojoules per mole at 25C.

(d)If the volume of the combustion container is 5.0 liters, calculate the final pressure in the container when the temperature is changed to 20.C. (Assume no oxygen remains unreacted and that all products are gaseous.)

Answers to selected problems : 6. 1.0 x 102 kJ 7. specific heat capacity (s) = .127 J/g°·C, molar heat cap. = 26.3 J/mol·°C 8. 59.4 °C 9. 0.49 J/g·°C 10. ΔH = -56 kJ/mol 11. ΔHf = -66 kJ/mol 12. 2.05 kJ/°C 13b. -725.9 kJ/mol 13c. -239.3 kJ 13d 0.90 atm