Temperature changes in reacting solutions sim
Pick one variable, mix the reactants in a lidded polystyrene cup, take readings every 30 seconds, correct for cooling, repeat, and see the temperature change level off when one reactant runs out.
Energetics: investigating the temperature change of reactions (AQA required practical 4) · covers the GCSE, IGCSE, O-Level (exothermic and endothermic only) topic
What the sim shows
An exothermic reaction gives out energy to the surroundings, so the solution warms; an endothermic reaction takes energy in, so it cools. In the required practical you measure the temperature change and investigate one variable at a time, keeping everything else the same. The polystyrene cup and lid cut heat loss, but some still leaks out while the reaction runs, so the highest (or lowest) reading is not the full change. Drawing the cooling line back to the moment of mixing corrects for this. For a fixed volume of solution, the temperature change grows as you add more of one reactant until the other one runs out; past that point it changes nothing more. (If instead you add more of a solution, the mixture gets bigger and ΔT goes down again.) Enthalpy changes (rounded, from data-book values): magnesium with acid −467 kJ/mol, zinc −154; sodium hydrogencarbonate with acid about +28; neutralisation −57 kJ/mol of water; displacement from copper(II) sulfate by magnesium −532, zinc −217, iron −154 kJ/mol. The solution is taken as water: 4.18 J/(g °C), 1.00 g/cm³. Time moves only when you press Wait 30 s. Model limits: the heat-loss rate (k = 0.0008 per second) and the reaction speeds are illustrative; above a 20 °C rise, real results are lower (the mixture froths and loses heat faster, and magnesium also fizzes in copper(II) sulfate); the cup itself absorbs no heat; the readings wobble by up to 0.2 °C so repeats differ; AQA does not ask you to calculate ΔH.
- Polystyrene cup and lid: cut heat loss
- Balance pan: the solid is weighed in the boat
- Probe and thermometer: readings every 30 s to 0.1 °C
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