When 23.6 g of calcium chloride, CaCl_2, was dissolved in water in a calorimeter
ID: 996465 • Letter: W
Question
When 23.6 g of calcium chloride, CaCl_2, was dissolved in water in a calorimeter, the temperature rose from 25.0degreeC to 38.7degreeC. If the heat capacity of the solution and the calorimeter is 1258 J/degreeC. what is the enthalpy change when 1.20 mol of calcium chloride dissolves in water? The solution process is CaCl_2(s) rightarrow Ca^2+(aq) + 2Cl^-(aq) 6.69 A sample of ethanol, C_2H_5OH, weighing 2.84 g was burned in an excess of oxygen in a bomb calorimeter. The temperature of the calorimeter rose from 25.00degreeC to 33.73degreeC. If the heat capacity of the calorimeter and contents was 9.63 kJ/degreeC, what is the value of q for burning 1 mol of ethanol at constant volume and 25.00degreeC? The reaction is C_2H_5OH(l) + 3O_2(g) rightarrow 2CO_2(g) + 3H_2O(l)Explanation / Answer
Theory.
q = msT
where:
q = heat change
m = mass of sustance
s = specific heat
T = temperature change
and
C = ms
where C is heat capacity.
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1. Data.
m = 23.6 gr
C = 1258 J/°C
T = (38.7 - 25.0)°C = 13.7°C
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Answer.
q = CT = 1258 J/°C x 13.7 °C
q = 17234.6 J = 17.2346 KJ
For 1.20 mol CaCl2 which m.wt is 110.98 g/mol = (110.98 g/1.20 mol)/(23.6 g) x 17.2346 KJ/mol
q = 67.5386 KJ
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2. Data.
2.84 g EtOH
T = (33.73 - 25.0)°C = 8.73°C
C = 9.63 KJ/°C
q = ??
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Answer.
q = CT = 9.63 KJ/°C x (8.73°C)
q = 84.07 KJ
If 2.84 g EtOH x (1 mol/46.07 g) = 0.0616 mol EtOH. So, 0.0616 mol EtOH x (84.07 KJ/mol EtOH) = 5.18 KJ
q = 5.18 KJ
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