Question

If a student performs an endothermic reaction in a calorimeter, how does the calculated value of ∆H differ from the actual value if the heat exchanged with the calorimeter is not taken into account?

Short answer

If the heat exchanged with the calorimeter is not taken into account, then ‘q_surr’ is very small, giving a calculated ΔH value also becoming less positive than it should be.

Step-by-step solution

Step 1: Calorimeter:

A device for measuring the heatevolvedduring a chemical reaction

and for calculating the heat capacity of the compounds.Calorimetry is used to measure amounts of heat transferred to or from a substance. To do so, the heat is exchanged with a calibrated object (calorimeter).

The change in temperature of the measuring part of the calorimeter is converted into the amount of heat

Step 2:

As we know that |q_surr| = |q_solution + q_cal|

Generally, we assume thatthecalorimeter is an adiabatic system.

Therefore,’qcal’ is zero (no heat gain/loss by the calorimeter).

However, if the calorimeter has a non-zero heat capacity, then some of the heat absorbed by the endothermic reaction came from the calorimeter.

Hence,if we ignore qcal, then ‘qsurr’ is very small, giving a calculated ΔH value is also become less positive than it should be.