Multiple Choice
The combustion of ethanol is shown below. C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g) ΔH = –1367 kJ mol–1. The enthalpy change for the combustion of 12.5 g of ethanol is:
8. Thermochemistry
Thermochemical Equations
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Two solutions, initially at 24.69°C, are mixed in a coffee cup calorimeter. When a 200.0 mL volume of 0.100 M AgNO3 solution is mixed with a 100.0 mL sample of 0.100 M NaCl solution, the temperature in the calorimeter rises to 25.16°C. Determine the enthalpy change (ΔH) for the reaction, assuming the specific heat capacity of the solution is 4.18 J/g°C and the density is 1.00 g/mL.
A
-3.14 kJ
B
-2.09 kJ
C
-1.05 kJ
D
-0.52 kJ
Verified step by step guidance1
Calculate the total volume of the mixed solution by adding the volumes of AgNO3 and NaCl solutions: 200.0 mL + 100.0 mL = 300.0 mL.
Determine the mass of the solution using the density (1.00 g/mL). Since the total volume is 300.0 mL, the mass is 300.0 g.
Calculate the temperature change (ΔT) by subtracting the initial temperature from the final temperature: ΔT = 25.16°C - 24.69°C.
Use the formula for heat absorbed or released: q = m × c × ΔT, where m is the mass, c is the specific heat capacity (4.18 J/g°C), and ΔT is the temperature change. Substitute the values to find q.
Convert the heat (q) from joules to kilojoules and determine the enthalpy change (ΔH) for the reaction. Since the reaction involves mixing solutions, the enthalpy change is equal to the negative of the heat absorbed or released: ΔH = -q.
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