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Energy ChangesIntroduction

The Currency of Chemical Reactions

Part of Bond Energies (HT) · GCSE GCSE Chemistry revision

This introduction covers The Currency of Chemical Reactions within Bond Energies (HT) for GCSE Chemistry. Revise Bond Energies (HT) in Energy Changes for GCSE Chemistry with 25 exam-style questions and 15 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 1 of 15 in this topic. Use this introduction to connect the idea to the wider topic before moving on to questions and flashcards.

Topic position

Section 1 of 15

Practice

25 questions

Recall

15 flashcards

📖 The Currency of Chemical Reactions

Think of bonds like bank accounts. Every bond has energy stored in it — like money saved up. To break a bond, you need to "spend" energy (it's endothermic). But when you make a new bond, you "earn" energy back (it's exothermic). Whether a reaction releases or absorbs energy overall depends on the balance sheet: did you spend more breaking old bonds, or earn more making new ones? This is the fundamental principle behind bond energy calculations — and it explains everything from why burning methane releases heat to why some reactions need continuous heating.
💰 The Bank Account Analogy

Bond energy is like a bank balance for the reaction! Breaking bonds = the reaction withdraws money (energy must be put IN). Making bonds = the reaction deposits money (energy is given OUT). If the reaction earns more than it spends — more energy released making bonds than was needed to break them — the reaction is exothermic overall. If it spends more than it earns, it is endothermic. Note: always count from the reaction's perspective. Breaking bonds costs the reaction energy (energy flows in from the surroundings); making bonds pays the reaction energy (energy flows out to the surroundings).

Keep building this topic

Read this section alongside the surrounding pages in Bond Energies (HT). That gives you the full topic sequence instead of a single isolated revision point.

Bond Energy VisualisedDeep Dive: Breaking and Making BondsHow It Works: Calculating Energy Change from Bond Energies

Practice Questions for Bond Energies (HT)

Which statement correctly describes the energy change when chemical bonds are broken?

  • A. Energy is released to the surroundings
  • B. Energy is absorbed from the surroundings
  • C. No energy change occurs
  • D. Energy may be released or absorbed depending on the bond
1 markfoundation

Explain how you would determine, from a bond energy calculation, whether a reaction is exothermic or endothermic.

2 marksstandard

Quick Recall Flashcards

What are the units for bond energy?
kJ/mol (kilojoules per mole)
What is bond energy?
The energy needed to break 1 mole of a particular bond

25 questions on Bond Energies (HT) — practise free

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