Download Specific Heat and Enthalpy Practice

Specific Heat and Enthalpy Practice
(pg. 536 for specific heats and pg. 549 for enthalpies)
Chemistry I Honors
1. When 12 g of a food was burned in a calorimeter, the 100. mL of water in the calorimeter
changed from 20.0C to 33.0C.
a. What is the mass of water?
b. What is the change in temperature?
c. Calculate the heat released from the food in kJ.
ANS: 5.43 kJ
2. 5.00 g of copper was heated from 20.0C to 80.0C.
a. How much energy was used to heat the Cu?
ANS: 116 J
3. If a 3.15 g ring is heated using 10.0 J, it’s temperature rises by 17.9C. Calculate the
specific heat capacity of the ring. Is the ring pure gold?
ANS: 0.177 J/g-ºC, No
4. Exothermic or Endothermic Reaction
a. KBrO3(s) + 42 kJ  KBrO3(aq)
ANS: Endo
b. 2 Mg(s) + O2(g)  2 MgO(s) + 1200 kJ
ANS: Exo
5. In an experiment, 1.50 g of propane (C3H8) was burned in a calorimeter with excess
oxygen to make liquid water and carbon dioxide. The 1000. mL of water in the
calorimeter rose from 23.0C to 44.2C.
a. Write the balanced equation for the combustion of propane.
b. Calculate the energy absorbed by water from propane in the calorimeter.
ANS: 88.6 kJ
c. Calculate the number of moles of propane.
ANS: 0.0340 mol
d. Using the energy released from propane (absorbed by water) and the amount of
moles, determine the amount of energy per mole of propane.
ANS: -2600 kJ/mol
e. Write and balance the formation reaction for carbon dioxide.
f. What is the enthalpy of formation for part e? Remember how many moles of CO2
you have.
ANS: -1180.5 kJ
g. Write and balance the formation reaction for liquid water.
h. What is the enthalpy of formation for part g? Remember how many moles of H2O
you have.
ANS: -1143.2 kJ
i. Write and balance the formation reaction for gaseous propane. The enthalpy of
formation for propane is -104.0 kJ/mol.
j. What is the enthalpy of formation for part i?
ANS: -104.0 kJ
k. Which equation needs to switch to match the final equation from part a)? What
happens to the sign for the enthalpy?
ANS: propane and becomes positive
l. Using Hess’s Law, cancel out molecules to write the final equation and calculate
the total enthalpy for the combustion of one mole of propane.
ANS: -2219.7 kJ/mol
m. Determine the percent error from part d and l.
ANS: 17.1%
6. 1 mole of ethane was combusted to produce water vapor and carbon dioxide.
a. Write the balanced combustion equation for ethane.
b. Underneath each molecule write the corresponding enthalpy of formation value
for each.
c. Multiply each enthalpy of formation by the number of moles for each molecule.
ANS: ethane (-169.4 kJ), water (-1450.8 kJ), carbon dioxide (-1574 kJ)
d. Using the equation of ΔH = ΣHproducts – ΣHreactants calculate the total enthalpy (ΔH)
for the combustion of 1 mole of ethane.
ANS: -1427.7 kJ