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Why is fire hot?

Why is fire hot?
Jake Bolger from Warwickshire (age 5-14)
Sonia Hussein from Stockton on Tees (aged 5-14)

Is it possible for fire to be cold?
Ashleigh Pinder from Stockton on Tees
Aged 5-14

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One Response

  1. Fire comes from burning something – let’s say wood – in air. This basically gets the molecules in the wood to combine or react with the oxygen molecules in the air, and we get fire, maybe some smoke or gases given off, some residue left over – wood ash in our example – and heat and light. The heat and light comes from energy given off by the burning reaction – which is the atoms in the wood and oxygen molecules getting mixed up and recombining in a different way to make the ash and smoke. The molecules of wood, oxygen, ash and smoke all have energy locked up inside them, but when it’s added up the wood and oxygen molecules have more energy inside them before they’re burnt than the ash and smoke molecules have afterwards – the difference in energy is what’s given off as heat and light. There’s a fancy name for any reaction – not just burning – that gives off heat – they are called ‘exothermic’.

    Fire or burning isn’t normally cold – the light in the flames you see is another form of the energy being given off – but you do get some reactions where the molecules afterwards have more energy than before – so they take heat in and cool down whatever’s around them. The fancy name for these is ‘endothermic’.

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