Summary notes for CIE IGCSE Biology Topic 7: Chemical reactions
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Course
Chemistry
Institution
GCSE
Complete revision notes for Topic 7 of the CIE IGCSE Chemistry course: Chemical reactions. Explanations with diagrams for every specification point. These notes are written for candidates taking the Extended paper.
Identify physical and chemical changes, and understand the differences between them
Physical change
Physical changes (such as melting or evaporating) do not produce any new chemical
substances.
These changes are often easy to reverse, and mixtures produced are usually relatively easy
to separate.
Chemical change
In chemical reactions, new chemical products are formed that have very different properties
to the reactants.
Most chemical reactions are impossible to reverse.
Energy changes also accompany chemical changes and energy can be given out (exothermic)
or taken in (endothermic).
The majority of chemical reactions are exothermic with only a small number being
endothermic.
7.2 Rate (speed) of reaction
Describe and explain the effect of concentration, particle size, catalysts (including enzymes)
and temperature on the rate of reactions
Concentration
Increase in the concentration of a solution, the rate of reaction will increase.
This is because there will be more reactant particles in a given volume, allowing more
frequent and successful collisions per second, increasing the rate of reaction.
,Compared to a reaction with a reactant at a low concentration, the graph line for the same
reaction but at a higher concentration has a steeper gradient at the start and becomes
horizontal sooner
This shows that with increased concentration of a solution, the rate of reaction will
increase
Particle size
Increase in the surface area of the solid, the rate of reaction will increase. This is because
more surface area particles will be exposed to the other reactant so there will be more
frequent and successful collisions per second, increasing the rate of reaction.
, Compared to a reaction with lumps of reactant, the graph line for the same reaction but
with powdered reactant has a steeper gradient at the start and becomes horizontal sooner
This shows that with increased surface area of the solid, the rate of reaction will
increase
Catalysts (including enzymes)
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