Over the Top!

Over the Top! Reaction profiles you can ride

This free game is part of our AQA GCSE Chemistry (8462) course for exams in EXAM YEARS 2027-2029.

What is a reaction profile?

A reaction profile (also called an energy level diagram) shows how the energy changes as a reaction proceeds. The vertical axis is energy and the horizontal axis is the progress of the reaction. A curved line starts at the energy of the reactants, rises to a peak and then falls to the energy of the products. For AQA GCSE Chemistry (spec point 4.5.1.2) you need to draw simple profiles for exothermic and endothermic reactions, showing the relative energies of the reactants and products, the activation energy and the overall energy change, and use a profile to say whether a reaction is exothermic or endothermic.

Over the Top! turns every profile into a roller coaster at Peak Park, a theme park at night. The height of the track is energy and the ride runs from the reactants’ station to the products’ station. A glass pod on the car holds the reacting particles, and at the top of the hill you watch their old bonds break and new bonds form as they turn into the products.

Activation energy: getting over the hill

Chemical reactions can only happen when particles collide with enough energy. The minimum energy they need is the activation energy. On a profile it is the height from the reactants’ level up to the top of the hill. In the game you hold LAUNCH and an energy column rises from the reactants. Let go too early and the car climbs part of the hill and rolls back unchanged: no reaction. Let go just after the column passes the top of the hill and you score a perfect launch, because you gave the reactants just enough energy. The column you build is exactly the activation energy arrow you draw in the exam.

Exothermic or endothermic?

In an exothermic reaction, energy is transferred to the surroundings, so the temperature of the surroundings goes up. Energy is conserved, so the products have less energy than the reactants and sit lower on the profile. Combustion, many oxidation reactions (such as a hand warmer), neutralisation and the reaction in a self-heating can are exothermic. In an endothermic reaction, energy is taken in from the surroundings, so their temperature goes down and the products sit higher. Thermal decompositions, the reaction of citric acid with sodium hydrogencarbonate and some sports injury packs are endothermic.

In the game you read a clue, such as a thermometer that falls from 20 °C to 14 °C, and drag the products’ platform lower or higher before you launch. When the car arrives, the crowd at the products’ station either warms up or frosts over, and a giant thermometer shows what happened to the surroundings.

Drawing the arrows and adding a catalyst

After each ride you label the profile like an exam answer by dragging an arrow from where it starts to where it ends. The activation energy arrow goes from the reactants’ level up to the top of the hill. The overall energy change arrow goes from the reactants’ level to the products’ level: down for exothermic, up for endothermic. Common mistakes, such as measuring the activation energy from the products or drawing the overall energy change from the peak, each open a short explanation with a link to the lesson. Exam profiles with values in kJ let you practise reading the levels: reactants at 50 kJ and a peak at 120 kJ give an activation energy of 70 kJ.

The catalyst level uses the Haber process and the decomposition of hydrogen peroxide. A catalyst provides a different pathway with a lower activation energy, shown as a dashed track. You drag its hill down while the reactants’ and products’ levels stay locked, because a catalyst does not change the overall energy change.

How to play

Hold LAUNCH, the space bar, or anywhere on the track, and let go when the energy column passes the dashed line at the top of the hill. Drag platforms and hilltops with a mouse or finger, or use the arrow keys, and press SET. Draw arrows by dragging, or tap two levels (keys 1, 2 and 3). Zara, the chief ride engineer, explains each new idea, and the game ends with a 60-second rush where you sort reactions as exothermic or endothermic and launch them as fast as you can. A game takes about 7 to 9 minutes, works on a computer, tablet or phone, and your best score is saved so you can play again.