Calculate enthalpy changes from calorimetry data using q = mcΔT, and interpret exothermic and endothermic reactions.

What this dot point is asking

You must classify reactions energetically and calculate enthalpy changes from experimental calorimetry data.

Exothermic and endothermic reactions

In an exothermic reaction the products are lower in energy than the reactants; in an endothermic reaction they are higher.

The calorimetry equation

Heat transferred to or from the water is:

where $m$ is the mass of water (g), $c$ is the specific heat capacity of water ($4.18\ \text{J g}^{-1}\,{}^\circ\text{C}^{-1}$), and $\Delta T$ is the temperature change ($^\circ\text{C}$).

To get the molar enthalpy change, divide $q$ by the moles of the limiting reactant:

The negative sign converts "heat gained by water" into "enthalpy of the reaction": if the water warmed, the reaction was exothermic ($\Delta H < 0$).

Sources of error in calorimetry

Simple calorimeters lose heat to the surroundings, so the measured temperature rise - and hence the calculated energy - is usually lower in magnitude than the true value. Incomplete combustion and heat absorbed by the container add further error.

Why this matters for managing processes

Knowing whether a process is exothermic or endothermic - and by how much - lets engineers design heating, cooling and safety systems, and (combined with Le Chatelier's principle) predict how temperature affects equilibrium yield.