Consider the reaction
C12H22O11(s) + 12 O2(g) → 12 CO2(g) + 11 H2O(l)
in which 10.0 g of sucrose, C12H22O11, was burned in a bomb calorimeter with a heat capacity of 7.50 kJ/°C.
The temperature increase inside the calorimeter was found to be 22.0° C. Calculate the change in internal energy, ΔE, for this reaction per mole of sucrose.
Express the change in internal energy in kilojoules per mole to three significant figures.
A calorimeter is an insulated device in which a chemical reaction is contained. By measuring the temperature change, ΔT, we can calculate the heat released or absorbed during the reaction using the following equation:
q = specific heat × mass × ΔT
Or, if the calorimeter has a predetermined heat capacity, C, the equation becomes
q = C × ΔT.
At constant pressure, the enthalpy change for the reaction, ΔH, is equal to the heat, qp; that is,
ΔH = qp
but it is usually expressed per mole of reactant and with a sign opposite to that of q for the surroundings. The total internal energy change, ΔE (sometimes referred to as ΔU), is the sum of heat, q, and work done, w:
ΔE = q + w
However, at constant volume (as with a bomb calorimeter) w = 0 and so ΔE = qv.
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