Energy Changes

Endothermic reactions
1. A reaction where energy is transferred in from the surroundings
2. Used for reactions that need to reduce temperature such as instant cold packs and Thermal decompositon reactions
3. Bond Breaking
Exothermic reactions
1. A reaction where energy from reaction is transferred to the surrondings
2. Used for: Combustion, oxidation, neutralisation reactions and hand warmers
3. Bond Making
Reaction Profiles
1. Can show relative difference in energy reactants and products on reaction profiles
2. Exothermic
  1. Energy released when new bonds are formed is greater thean energy required when bonds are broken
3. Endothermic
  1. Activation energy needed to start reaction
  2. Energy released when new bonds are formed is less than energy needed to when bonds are broken
Bond Energy calculations
1. Energy must be supplied to create or break bonds
2. Can calculate overall energy change through bond energies
Chemical Cells and batteries
1. Metals tend to lose electrons to form postive ions
2. When two metals are dipped into a salt solution and joined by a wire the more reactive metal will donate electrons to the less reactive metal
3. The Greater the difference in reactivity between metals the more voltage produced
4. Non renewable batteries stop working when one of the reactants is used up while Rechargeable batteries use reverse reactions to regenerate the product to its original form
Fuel cells
1. Most of world relies on fossil fuels
2. Hydrogen can be alternate (can be burnt in combustion engines or used to power verichles
3. Hydrogen gas can be oxidised to provide a source of electrons to the hydrogen fuel cell - waste product is water
4. Hydrogen is highly flammable, sometimes produced by unrenewable means and is difficult to store

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