Energy changes in reactions, exothermic and endothermic reactions, energy profile diagrams, bond breaking and making, and calculating heat changes from experiments.
5 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.
A campfire releases heat, while a cold pack for an injury absorbs it. Both are chemical reactions, and their energy diagrams are mirror images.
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Copy these into your notebook in your own words — that is how they stick.
Releases energy; temperature rises; ΔH negative; products lower in energy.
Absorbs energy; temperature falls; ΔH positive; products higher in energy.
Minimum energy needed to start the reaction.
Breaking absorbs energy; making releases energy.
m = mass of water/solution (g); c = 4.2 J/g °C.
q ÷ moles (convert J to kJ); negative if the temperature rises.
Makes the experimental ΔH smaller than the true value.
Lowers Eₐ; ΔH unchanged.
3 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness. More games in the Chemistry Arcade.
8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better. Work each item on paper first.
Write full answers, then reveal the mark scheme and tick the points you earned (15 marks in total). Show all your working — method marks count. Your answers are saved on this device.
Question 1 [15 marks]
50.0 cm³ of 1.00 mol/dm³ sodium hydroxide at 25.0 °C is added to 50.0 cm³ of 1.00 mol/dm³ hydrochloric acid at 25.0 °C in a polystyrene cup. The highest temperature reached is 31.5 °C. Take the density of the solution as 1.00 g/cm³ and c = 4.2 J/g °C.
(a) (a) State whether the reaction is exothermic or endothermic, with a reason. [2]
(b) (b) Calculate the heat energy transferred to the solution. [3]
(c) (c) Calculate the number of moles of acid that reacted. [2]
(d) (d) Calculate the enthalpy change of neutralisation in kJ/mol. [3]
(e) (e) Sketch an energy profile diagram for this reaction. [3]
(f) (f) State one source of error and one improvement. [2]
Find these in your own past-paper booklets for extra timed practice. Items above are written in the style of these papers; any adapted from a specific question say so.