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Calorimetry Practice Questions
1. A 1.75 g sample of acetic acid, CH3CO2H, was burned in oxygen in a calorimeter. calorimeter. The calorimeter contained 925 g of water and had a heat capacity of 2.53 kJ/ oC. The temperature temperature of the calorimeter and its contents increased from 22.2 oC to 26.5 oC. What is the molar heat of combustion of acetic acid? Answer: Acetic acid
Calorimetry Practice Questions 2. A 3.5 g sample of quinine, C6H4O2, was burned in a calorimeter with a heat capacity of 3.43 kJ/ oC and contained 1.2 kg of water. The temperature of the calorimeter and water increased from 19.0 oC to 28.0 oC. a) What is the molar enthalpy of combustion of quinine? Answer: Quinine m = 3.5 g mm = 108.09 g/mol
b) What is the specific enthalpy of combustion of quinine? ∆Hcombustion quinine = -76.0 kJ/3.5 g = -22 kJ/g
c) Write the thermochemical equation that represents the reaction. C6H4O2 + 6O2 6CO2 + 2H2O + 2350 kJ
Water m = 1200 g c = 4.18 J/goC ∆T = 9.0 oC
Calorimetry Practice Questions 3. The combustion of 1.00 mol of glucose, C 6H12O6, releases 2820 kJ of heat. If 2.0 g of glucose is burned in a calorimeter containing 1.0 kg of water, and the temperature increases by 3.5 oC, what is the heat capacity of the calorimeter? Answer: Glucose m = 2.0 g mm = 180.16 g/mol n = 2.0/180.16 = 0.0111 mol ∆H = -2820 kJ/mol
Calorimeter C=? ∆T =3.5 oC
qglucose = n∆H = (0.0111)(2820) = 31.3 kJ or 31300J
q glucose = qcalorimeter + qwater 31300 = C∆T + mc ∆T 31300 = C(3.5 oC) + (1000 g)( 4.18 J/goC)( 3.5 oC) 3.5 C = 116 670 C = 4760 J/oC or 4.8 kJ/oC
Water m = 1000 g c = 4.18 J/goC ∆T = 3.5 oC
Calorimetry Practice Questions 4. The molar heat of combustion of sucrose, C 12H22O11, liberates 5650 kJ of heat. A 100 g calorimeter with a specific heat capacity of 17.5 J/goC contains 500 g of water. How many grams of sucrose would have to be burned to increase the temperature of the water and calorimeter by 4.5oC?
∆H = q/n n = q/ ∆H = 17.3/5650 = 0.00306 mol m = n x mm =( 0.00305)(342.30) = 1.05 g
Water m = 500 g c = 4.18 J/goC ∆T = 4.5 oC
Calorimetry Practice Questions 5. A 2.56 g sample of anthracene, C4H10, was burned in a calorimeter with a heat capacity of 0.428 kJ/oC. The calorimeter was immersed in 1500 mL of water. If the molar heat of combustion of anthracene is -2400 kJ/mol, what would the final temperature of the water and calorimeter be if the initial temperature is 22.4 oC?
Answer: Anthracene m = 2.56 g mm = 58.12 g/mol
∆H = -2400 kJ/mol
Calorimeter C = 0.428 kJ/oC T i = 22.4 oC T f = ? ∆T =? oC
Water v = 1500 mL D = 1.0 g/mL m = 1500 g c = 4.18 J/goC ∆T = ? oC
nanthracene = 2.56/58.12 = 0.0440 mol qanthracene = n ∆H = (0.0440)(2400) = 105.6 kJ or 105600J
qanthracene = qcalorimeter + qwater 105600 = C∆T + mc ∆T 105600 = (428) ∆T + (1500 g)( 4.18 J/goC) ∆T 105600 = 6698 ∆T ∆T = 15.8 oC Since the reaction is exothermic, the temperature of the calorimeter and the water will increase. Therefore T f = 22.4 + 15.8 = 38.2 oC
Calorimetry Practice Questions 6. Consider the following reaction: C + O2
CO2 + 388.8 kJ
a) What quantity of heat will be released when 3.0 g of carbon burns? Answer: ∆H = -388 kJ/mol of Carbon
nC = 3.0/12.01 = 0.250 mol
∆H = q/n q = n ∆H = (0.250)(388) = 97.2 kJ Therefore 97.2 kJ will be released or 97 200J.
b) If the combustion of carbon takes place in a 1.3 kg calorimeter that is immersed in 1850 g of water, the temperature of the system changes by 11.8 oC. What is the specific heat capacity of the calorimeter? Calorimeter
