A student uses a sparkler on Bonfire Night. The sparkler glows brightly and gives out a large amount of heat as it burns. Explain why the sparkler feels hot and describe what this tells us about the bonds broken and bonds formed during the reaction.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Sparklers contain a metal fuel that reacts with oxygen in the air when ignited. The reaction releases energy to the surroundings.
Model answer (4 marks)
The sparkler reaction is exothermic, so it releases energy to the surroundings.
The released energy raises the temperature of the sparkler and the air around it, which is why it feels hot.
During the reaction, the bonds in the metal fuel and oxygen are broken, but the bonds formed in the combustion products (e.g. metal oxides) release more energy than was required to break the original bonds.
Thus, bond making is an exothermic process and bond breaking is endothermic, giving a net release of energy.
The released energy raises the temperature of the sparkler and the air around it, which is why it feels hot.
During the reaction, the bonds in the metal fuel and oxygen are broken, but the bonds formed in the combustion products (e.g. metal oxides) release more energy than was required to break the original bonds.
Thus, bond making is an exothermic process and bond breaking is endothermic, giving a net release of energy.
Examiner tips
- Use the word "exothermic" to show understanding of energy flow.
- Explain that heat rises temperature of surroundings.
- Mention that more energy is released in bond formation than is consumed in bond breaking.
- Show the link between bond making being exothermic and the sparkler feeling hot.
Common mistakes
- Saying the reaction is endothermic or that it absorbs heat.
- Forgetting to explain the temperature rise of the surroundings.
- Confusing the terms bond making with bond breaking.
Mark scheme (4 marks)
- The reaction is exothermic
- Energy is transferred to the surroundings, causing the temperature of the surroundings to increase
- More energy is released when bonds are formed in the products than is required to break bonds in the reactants
- Bond making is an exothermic process (and bond breaking is an endothermic process)
Related
- All OCR GCSE Chemistry A: Gateway Science (J248) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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