Endo/Exoothermic Reactions

Chemical reaction

A process where reactants change into products by breaking and forming bonds

Evidence of a chemical reaction

Colour change; temperature change; gas produced; precipitate formed; light produced; light given off

Exothermic reaction

A reaction that releases energy to the surroundings; temperature increases

Endothermic reaction

A reaction that absorbs energy from the surroundings; temperature decreases

Meaning of exo

Out (as in exit)

Meaning of en/endo

In (as in entrance)

Meaning of -thermic

Relating to heat

Most common reaction type

Most chemical reactions are exothermic

Reaction profile

A diagram showing energy changes of reactants and products during a reaction

Exothermic reaction profile key feature

Products have less energy than the reactants

Energy change in exothermic reactions (ΔH)

Negative

Endothermic reaction profile key feature

Products have more energy than the reactants

Energy change in endothermic reactions (ΔH)

Positive

Why some reactions get hotter

Energy is released to the surroundings (exothermic)

Why some reactions get colder

Energy is taken in from the surroundings (endothermic)

Activation energy

The minimum amount of energy needed for a chemical reaction to take place

What happens if particles collide with less than activation energy

They just bounce off each other and no reaction occurs

Bond breaking

Endothermic; energy is absorbed from the surroundings

Bond making

Exothermic; energy is released to the surroundings

Example exothermic reaction

H₂ + Cl₂ → 2HCl

Example endothermic change

H₂O(g) → H₂O(l)

Activation energy on a reaction profile

Arrow drawn from the reactants up to the peak of the curve

Energy transfer in an exothermic reaction

Energy is transferred from the reaction to the surroundings

Energy transfer in an endothermic reaction

Energy is transferred from the surroundings into the reaction