Energy transfer in reactions

exothermic

• A reaction that gives energy out, out, usually in the form of heat. Usually shown by a riserise in temperature

• E.g. burning fuels, neutralisation, adding water to anhydrous copper sulphate

endothermic

• A reaction that takes inin energy from the surroundings. Usually shown by a fallfall in temperature

• E.g photosynthesis, ammonium nitrate and water, decomposition of calcium carbonate or malachite (copper carbonate)

Rearrangement of atoms (HT)(HT)

• In a reaction, reactants are turned into productsproducts

• In order to do this, the atoms of the reactants must be pulled apart by breaking the bonds between them.

• Bonds between the atoms of the new products must then be made

(HT)(HT)

reactants atoms products

Carbon

And oxygen

Carbon dioxide

Bonds made

Bonds broken

Breaking and making (HT)(HT)

• Energy is needed to break bonds

• And is released when bonds are made

• Breaking bonds is endothermic• Making bonds is exothermic

Energy changes (HT)(HT)

• In an exothermic reaction, more energy is released by making bonds in the products than by breaking bonds in the reactants

• In an endothermic reaction, more energy is needed to break bonds in the reactants than is released by making bonds in the products