Specific Heat Capacity and Calorimetry Practice Problems
(*** specific heat capacities of substances are found in text page 292)
1. If the same amount of heat were added to individual 1-g samples of water, methanol, and aluminum, which substance would undergo the greatest temperature change? Explain.
2. How many joules of energy are needed to raise the temperature of 255g of ice from –26oC to –5oC ? (1.1 X 104 J)
3. A sample of ethanol absorbs 23.4 KJ of energy. The temperature increases from 5.6oC to 19.8oC. What is the mass of the sample if the specific heat capacity of ethanol is 2.46 J/goC)? (670 g)
4. If 5.00g of anhydrous calcium chloride (CaCl2) is dissolved in 100.0mL of water in a coffee cup calorimeter,
a. Calculate the enthalpy change, given that the temperature changed from 34.0oC to 23.0oC. (+4.60 kJ)
b. Calculate the molar enthalpy of solution of CaCl2. (+102 kJ/mol)
5. A chemist wants to determine empirically the enthalpy change for the following reaction:
Mg (s) + 2HCl(aq) à MgCl2 (aq) + H2 (g)
The chemist uses a coffee-cup calorimeter to react 0.50 g of magnesium ribbon with 100.0 mL of 1.00 M HCl (aq) . The initial temperature of the HCl is 20.4 oC. After neutralization, the highest recorded temperature is 40.7 oC. Calculate the enthalpy change in kJ/mol of Mg for this reaction.(-4.1 X 102 kJ/mol)
6. HCl(aq) + NaOH (aq) à H2O (l) + NaCl (aq) + 2400 kJ
50.0mL of 0.10 mol/L HCl at 23.5oC is added to 50.0mL of 0.10 mol/L NaOH at the same temperature. What will be the final temperature of the reaction? ( 52 oC)
7. A sample of ethanol, C2H5OH, is burned in an aluminum can calorimeter, having a mass of 50.0g.
a. Identify the system and the surroundings
b. What is the quantity of heat gained by the water in the calorimeter and the calorimeter, if it contained 150.0g of water and the temperature changed from 23.0oC to 43.0oC. (13500J)
c. What is the enthalpy change for the reaction? (-13500J)
d. The molar enthalpy of combustion of ethanol is –1368 kJ/mol. What mass of ethanol was in the calorimeter? (0.453 g)
8. The molar enthalpy of combustion of methane is -803 kJ/mol. What is the minimum mass of methane that must be burned to warm 4.00 L of water from 22.4 C to 87.6 C, assuming no heat losses. (21.8 g)
9. Indicate whether the reactions in questions 4-8 are exothermic or endothermic.
Challenger:
10. The fermentation of glucose to form ethanol and carbon dioxide is an exothermic process:
C6H12O6 (aq) à 2 C2H5OH(aq) + 2 CO2 (g) DH = - 98.5 kJ
10.0 L of grape juice with a glucose concentration of 200.0 g/L is fermented in an insulated tank.
Calculate the theoretical temperature increase of the solution brought about by the fermentation of this amount of glucose. State any two assumptions that you have made in your calculation. (26.1 oC)