CK-12-Chemistry Intermediate

17.2. Thermochemical Equations http://www.ck12.org

2. Why is a foam cup used as a calorimeter rather than a glass beaker?


3. What are some possible sources of error that would be present in an experiment where a foam cup is used as
   a calorimeter?


4. When 1 mol of nitrogen gas reacts with 3 mol of hydrogen gas, 2 mol of ammonia gas is produced and 92.6
   kJ of heat is released. Write the thermochemical equation.

Problems

5. Given the following reaction for the formation of water from hydrogen and oxygen gases: What is the∆H for
   the following reactions?
   a. H 2 (g)+ 1 /2O 2 (g)→H 2 O(l)
   b. 2H 2 O(l)→2H 2 (g)+O 2 (g)


6. 
   
   
   
   100. mL of 0.500 M HCl is mixed with 100. mL of 0.500 M NaOH in a foam cup calorimeter. The
        initial temperatures of both solutions are 22.50°C. After the reaction occurs, the temperature rises to 26.00°C.
        Calculate the enthalpy change for the reaction. Assume the densities of the solutions are 1.00 g/mL and the
        specific heat is 4.18 J/g°C.
   
   
   
   


7. An ice cube is dropped into a foam cup calorimeter containing 95.0 mL of water at 20.0°C. The temperature
   drops to 13.7°C as the ice cube melts. How much total heat (in kJ) was released by the water into the ice cube?


8. 66.80 g of lead is heated to 155°C and then placed into a foam cup calorimeter containing 70.0 mL of water
   at 15.2°C. Assuming no heat loss, calculate the final temperature of the water and lead.


9. Given the balanced equation below for the highly exothermic reaction of aluminum with oxygen to form
   aluminum oxide:
   a. What is the value of∆H when 1.00 mol of aluminum reacts?
   b. What is the value of∆H when 5.23 g of aluminum reacts?
   c. What is the value of∆H when 6.17 L of oxygen gas at STP reacts with excess aluminum?
   d. A certain reaction releases 6881 kJ of heat. What mass of aluminum oxide was produced in the reaction?


10. Propane gas combusts according to the following equation. 45.1 L of propane at 0.915 atm is combusted at
    513.°C. How much heat is released in the reaction? Assume the propane is an ideal gas.

Further Reading / Supplemental Links

• Enthalpy, http://www.wisc-online.com/Objects/ViewObject.aspx?ID=GCH8805


• TheThermochemicalEquation, http://science.widener.edu/svb/tutorial/thermoequationscsn7.html

Points to Consider

Enthalpy changes always accompany changes in state.

• What are the heat of fusion and heat of vaporization, and how can they be used to solve problems?


• What is the heat of solution?