Chemistry C2.4 and 5 Notes for Exam

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Chemistry Unit 2

Rate of Reaction C.4

The rate of a chemical reaction can be found by measuring the amount of a reactant used or the amount of product formed over time:

Rate of reaction = amount of reactant used / time

or

Rate of reaction = amount of product formed / time

Chemical reactions only occur when reacting particles collide with each other and with sufficient energy

The minimum amount of energy particles must have to react is called the activation energy

Increasing the temperature increases the speed of the reacting particles so that they collide more frequently and more energetically - this increases the rate of reaction.

Increasing the pressure of reacting gases increases the frequency of collisions and so increases the rate of reaction.

Increasing the concentration of reactants in solutions increases the frequency of collisions and so increases the rate of reaction.

Increasing the surface area of solid reactants increases the frequency of collisions and so increases the rate of reaction

Catalysts change the rate of chemical reactions but are not used up during the reaction

Different reactions need different catalysts

Catalysts are important in increasing the rates of chemical reactions used in industrial processes to reduce costs

Exothermic and Endothermic Reactions C.5

Chemical reactions involve energy transfers

Many chemical reactions involve the release of energy

For other chemical reactions to occur, energy must be supplied

When chemical reactions occur, energy is transferred to or from the surroundings

E X O T H E R M I C reactions is one that transfers energy to the surroundings.

exothermic reactions include combustion, many oxidation reactions and neutralisation

everyday uses of exothermic reactions include self-heating cans (eg for coffee) and hand warmers

E N D O T H E R M I C reactions take in energy from the surroundings.

endothermic reactions include thermal decompositions

some sports injury packs are based upon endothermic reactions

R E V E R S I B L E reactions are exothermic in one direction AND it is endothermic in the opposite direction.

the same amount of energy is transferred in each case

for example heating blue copper sulphate crystals:

hydrated copper sulfate (blue) anhydrous copper sulfate (white) + water

Right to Left Left to Right