IB Chemistry R1.1 Measuring Enthalpy Change Questionbank

In an experiment to determine $\Delta H$ for a neutralization reaction, which of the following must be measured?

If 0.050 mol of a substance releases 1.25 kJ of energy on combustion, what is the molar enthalpy change?

A student burns ethanol in a simple calorimeter and observes a sharp temperature increase in the surrounding water.

(a) State whether the combustion of ethanol is exothermic or endothermic.

(b) Sketch an energy profile diagram for this reaction.

(c) Label the activation energy, reactants, and products on your diagram.

(d) Explain, using bond enthalpies, why combustion reactions are typically exothermic.

The solution is non-aqueous

No heat is lost from the calorimeter to the surroundings

Enthalpy change is always negative

The system is open

$\Delta H > 0$, endothermic

$\Delta H < 0$, exothermic

$\Delta H = 0$, no heat exchanged

Cannot determine without pressure data

Volume, temperature change, concentration

Mass of acid and base, pressure

Volume of gas released

Change in pH

$+25.0\ \text{kJ mol}^{-1}$

$-25.0\ \text{kJ mol}^{-1}$

$+0.625\ \text{kJ mol}^{-1}$

$-0.625\ \text{kJ mol}^{-1}$

(e) The student suggests using propane instead of ethanol. Predict how the temperature change in the water might differ and justify your answer.