TEMPERATURE CHANGES

-these give out heat energy. 

- most chemical reactions are exothermic.

-The heat energy given out raises the temperature of surroundings. 

example of an exothermic reaction:

METHANE + OXYGEN --> CARBON DIOXIDE AND WATER

CH4 + 2O2 --> C02 + 2H20

explosions are exothermic reactions that release a lot of heat energy and gases v.v.v.v quickly.

These reactions take in heat energy.

- Not many chemical reactions are endothermic. 

- The reaction takes away heat energy from its surroundings, and so they feel cold once the reaction has taken place.

examples of endothermic reactions: 

Reacting sodium hydrgencarbonate with hydrochloric acid. 

and 

Dissolving ammonium nitrate in water.

bonds in reactants are BROKEN - these are endothermic.

In endothermic reactions, more energy is needed than is produced so the remaining needed energy is absorbed from the surroundings as heat energy.

new bonds in the products are FORMED- these are exothermic.

In exothermic reactions, less energy is needed than is produced and so the rest of the energy is released into the surroudings as heat energy.

exothermic:

endothermic: