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1. After coming in from outside, a student makes a cup of instant hot chocolate by heating water in a microwave. What is the gain in thermal energy if a cup (250 mL) of tap water is increased in temperature from 15 °C to 95 °C? (2 marks)
2. A backpacker uses an uncovered pot to heat 1.0 L of lake water on a single-burner stove. If the water temperature rises from 5.0 °C to 97.0 °C, what is the gain in thermal energy of the water? (2 marks)
3. Methanol is one type of fuel that is used in fondue heaters. In an experiment using a simple tin can calorimeter, 2.98 g of methanol was burned to raise the temperature of 650 g of water by 20.9 °C. Using this evidence, calculate the molar enthalpy of combustion of methanol (to produce water as a vapour). △cHm? (4 marks)
4. Write the symbols for the following terms. (4 marks)
(a) enthalpy of formation
(b) enthalpy of decomposition
(c) molar enthalpy of formation
(d) molar enthalpy of decomposition
5. Ethane is a component of natural gas. If the molar enthalpy of combustion of ethane is -1.56 MJ/mol, calculate the quantity of thermal energy gained by the burning of:
(a) 5.0 mol of ethane
(b) 40.0 g of ethane (4 marks)
6. In a laboratory investigation into the reaction Ba(NO3)2(s) + K2SO4(aq) → BaSO4(s) +2 KNO3(aq) a researcher adds a 261 g sample of barium nitrate to 2.0 L of potassium sulfate solution in a polystyrene calorimeter. Calculate of the molar enthalpy of reaction of barium nitrate.
Evidence As the barium nitrate dissolves, a precipitate is immediately formed. t1= 26.0 °C, t2 =29.1 °C. (2 marks)
7. Calculate the standard enthalpy change for reaction (1)
(1) H2O(g) + C(s) → CO(g) + H2(g) △r H° = ?
—the gasification of coal—from the following chemical equations and standard enthalpy changes using next reactions? (4 marks)
2C(s) + O2(g) → 2CO(g) fH° = -221.0 kJ
2H2(g) + O2(g) → 2H2O(g) fH° = -483.6 kJ
8. Calculate the standard enthalpy change for reaction (2)
(2) CO(g) + H2(g) + O2(g) → CO2(g) + H2O(g) △c H° = ?
—the combustion of coal gas— from the following information. (4 marks)
2C(s) +O2(g) → 2CO(g) fH° =-221.0 kJ
C(s) +O2(g) → CO2(g) fH° =-393.5 kJ
2H2(g) + O2(g) → 2H2O(g) fH° =-483.6 kJ
Answers
Answer:
3. Methanol is one type of fuel that is used in fondue heaters. In an experiment using a simple tin can calorimeter, 2.98 g of methanol was burned to raise the temperature of 650 g of water by 20.9 °C. Using this evidence, calculate the molar enthalpy of combustion of methanol (to produce water as a vapour). △cHm? (4 marks)
mwater=650g Q=mc△t
△t=20.9°C Q=(650g)(4.19)(20.9°C)
Cwater=4.19J/g .°C Q=56921.15 J
4. Write the symbols for the following terms. (4 marks)
(a) enthalpy of formation is △H°f
(b) enthalpy of decomposition is △decH°
(c) molar enthalpy of formation is △fHm
(d) molar enthalpy of decomposition is △decHM
5. Ethane is a component of natural gas. If the molar enthalpy of combustion of ethane is -1.56 MJ/mol, calculate the quantity of thermal energy gained by the burning of:
(a) 5.0 mol of ethane
ΔH = -1.56 MJ/mol Q = ΔHxn
= (-1.56)(5)
= -7.8 MJ or 7.8 MJ of energy released
(b) 40.0 g of ethane (4 marks)
ΔH = -1.56 MJ/mol n = m/M Q = ΔHxn
M = 30.0 g/mol = 40/30 = (-1.56)(1.33)
m = 40 g = 1.33 mol =2.075 MJ or 2.075 MJ released
6. In a laboratory investigation into the reaction Ba(NO3)2(s) + K2SO4(aq) → BaSO4(s) +2 KNO3(aq) a researcher adds a 261 g sample of barium nitrate to 2.0 L of potassium sulfate solution in a polystyrene calorimeter. Calculate of the molar enthalpy of reaction of barium nitrate.
Evidence As the barium nitrate dissolves, a precipitate is immediately formed. t1= 26.0 °C, t2 =29.1 °C. (2 marks)
T1 = 26.0°C ΔT = T2-T1 Q = mΔTc ΔH = Q/n
T2 = 29.1°C = 29.1-26.0 = (2)(3.1)(4.184) = -25.94/1
m = 2.0 kg = 3.1°C = 25.94 kJ = -25.94 kJ/mol
c = 4.184 kJ/kg°C Qrx = -25.94 kJ
M = 261.3 g/mol n = m/M
= 261/261.3
= 1.0 mol
Explanation: