End of Chapter Problems

Test your skills on the following problems.

Energy Changes

System and Surroundings

Example: An unknown gas expands in a container increasing the volume from 8.7 L to 18.9 L at a constant pressure of 1380 mmHg.

(a) Calculate the work done (in J) by the gas as it expands. (1 L· atm = 101.3 J).

(b) Calculate the internal energy of the system if the system absorbs 235.5 J of energy.

(c) Calculate the internal energy of the system if work was done against a vacuum. (1 L · atm = 101.3 J).

5m

Calorimetry

Example: Calculate the amount of heat absorbed when 12.0 g of water is heated from 20oC to 100oC. (c = 4.184 J/g· oC).

2m

Example: 101.3 g of an unknown metal has an initial temperature of 25oC. If it absorbs 639.1 J of energy to obtain a final temperature of 32.01oC identify the unknown metal.

4m

Example: Which substance has the highest molar heat capacity?

a) Copper (specific heat Cu (s): 0.39 J/g · oC)

b) Silver (specific heat Ag (s): 0.23 J/g · oC)

c) Iron (specific heat Fe(s): 0.46 J/g · oC)

d) Lead (specific heat Pb (s): 0.13 J/g · oC)

3m

Example: 25.00 g of heated metal ore is placed into an insulated beaker containing 615.5 g of water at 42.18oC. If the metal gains 19.11 kJ of energy, what is the final temperature of the water? (cwater = 4.184 J/g · oC).

5m

Example: If 53.2 g Al at 25.0 oC is placed in 110.0 g H2O at 90 oC, what is the final temperature of the mixture? The specific heat capacities of water and aluminum are 4.184 J/g · oC and 0.897 J/g · oC, respectively.

7m

Example: A 20.0 g sample of iron, specific heat Fe (s) = 0.46 J/g⋅oC, has an initial temperature of 30.2 oC. If 0.310 kJ are applied to the iron sample, calculate its final temperature.

4m

Example: A sample of H2O (l) containing 2.50 moles has a final temperature of 45.0 oC. If the sample absorbs 3.00 kJ of

heat, what is the initial temperature of the H2O (l)? The specific heat of H2O (l) is 4.184 J/g⋅ oC .

4m

Example: Determine the heat released when 80.0 g H2O (l) at 90 oC is cooled to ice at – 10.0 oC. Specific Heat of H2O (l) = 4.184 J / g⋅oC. Specific Heat of H2O (s) = 2.09 J / g⋅oC. Heat of Fusion of water = 333 J/g .

9m

Example: If 1050 g of aluminum metal with a specific heat capacity of 0.902 J/g⋅oat – 20 oC is placed in liquid water at 0.00 oC, how many grams of liquid water are frozen by the time that the aluminum metal has warmed to – 10 oC? Heat of Fusion of water = 333 J/g.

5m

Thermochemical Reactions

Hess's Law