keywords key phrases
C7 Energy Changes
C7.1 - Exothermic and Endothermic Reactions
Exothermic Reactions: chemical reactions that transfer energy from the chemicals to
the surroundings (eg. combustion, neutralisation)
Endothermic Reactions: chemical reactions that transfer energy to the chemicals from
the surroundings (eg. thermal decomposition, reaction of citric acid and sodium
hydrogen carbonate)
❖ In exothermic reactions, the energy of the reactants is higher than the energy of
the products, as energy is given to the surroundings
❖ In endothermic reactions, the energy of the reactants is lower than the energy of
the products, as energy is absorbed from the surroundings
C7.2 - Using Energy Transfers from Reactions
❖ exothermic reactions can be used in things like warm packs or self-heating cans,
as they release energy to heat up the surroundings:
single-use hand warmers reusable hand warmers
iron turns into hydrated iron oxide in the a supersaturated sodium ethanoate-water
exothermic reaction, as sodium chloride solution is placed in a plastic pack with a
acting as the catalyst metal disk, and when pressed, the metal
disk starts the exothermic reaction and
the sodium ethanoate recrystallise
❖ in self-heating cans, the typical equation is:
, keywords key phrases
❖ endothermic reactions can be used in things like ice packs, as they take energy
from the surroundings, cooling it:
➢ chemical cold packs normally contain ammonium nitrate and water,
which are combined from their separate packs when needed to carry out
the endothermic reaction
C7.3 - Reaction Profiles
❖ energy is released to the surroundings in exothermic reactions, so the products
have lower energy levels than the reactants:
❖ energy is taken in from the surroundings in endothermic reactions, so the
products have a higher energy level than the reactants:
C7 Energy Changes
C7.1 - Exothermic and Endothermic Reactions
Exothermic Reactions: chemical reactions that transfer energy from the chemicals to
the surroundings (eg. combustion, neutralisation)
Endothermic Reactions: chemical reactions that transfer energy to the chemicals from
the surroundings (eg. thermal decomposition, reaction of citric acid and sodium
hydrogen carbonate)
❖ In exothermic reactions, the energy of the reactants is higher than the energy of
the products, as energy is given to the surroundings
❖ In endothermic reactions, the energy of the reactants is lower than the energy of
the products, as energy is absorbed from the surroundings
C7.2 - Using Energy Transfers from Reactions
❖ exothermic reactions can be used in things like warm packs or self-heating cans,
as they release energy to heat up the surroundings:
single-use hand warmers reusable hand warmers
iron turns into hydrated iron oxide in the a supersaturated sodium ethanoate-water
exothermic reaction, as sodium chloride solution is placed in a plastic pack with a
acting as the catalyst metal disk, and when pressed, the metal
disk starts the exothermic reaction and
the sodium ethanoate recrystallise
❖ in self-heating cans, the typical equation is:
, keywords key phrases
❖ endothermic reactions can be used in things like ice packs, as they take energy
from the surroundings, cooling it:
➢ chemical cold packs normally contain ammonium nitrate and water,
which are combined from their separate packs when needed to carry out
the endothermic reaction
C7.3 - Reaction Profiles
❖ energy is released to the surroundings in exothermic reactions, so the products
have lower energy levels than the reactants:
❖ energy is taken in from the surroundings in endothermic reactions, so the
products have a higher energy level than the reactants:
