C2b Topic 5 - Chemical Reactions
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Energy is released when new bonds are formed - so bond formation is an _____________ process.
Exothermic!
In an EXOTHERMIC reaction, the heat energy released in forming bonds in the products is ___________ than the energy used in breaking old bonds in the reactants.
Greater!
An EXOTHERMIC reaction is one which overall
GIVES OUT ENERGY to the surroundings in the form of heat, shown by a RISE IN TEMPERATURE.
In an ENDOTHERMIC reaction, the energy required to break old bonds in the reactants is ___________ than the heat energy released when new bonds are formed in the products.
Greater!
An ENDOTHERMIC reaction is one which overall
TAKES IN ENERGY from the surroundings in the form of heat, shown by a FALL IN TEMPERATURE.
In an EXOTHERMIC reaction, energy is
GIVEN OUT
In an ENDOTHERMIC reaction, energy is
TAKEN IN
Examples of endothermic reactions
1) Photosynthesis uses light energy from the sun to convert carbon dioxide and water into glucose and oxygen. 2) As ammonium nitrate dissolves in water it takes in heat energy from its surroundings.
In an EXOTHERMIC REACTION the products are at a ___________ energy than the reactants
Lower!
In an ENDOTHERMIC REACTION the products are at a _____________ energy than the reactants
Higher!
Rate of reaction depends on four things
1) Temperature 2) Concentration - (or pressure for gasses) 3) Catalyst 4) Surface area of solid - (or size of particles)
A catalyst
Is a substance that changes the speed of a reaction, without being used up in the reaction.
A catalyst works by
1) Lowering the activation energy 2) This makes it easier for the reaction to happen and increases the rate of reaction 3) This means that a lower temperature can be used without the rate of reaction dropping
Why are catalytic converters used in vehicle exhausts
1) Vehicle exhausts can give off poisonous gases like carbon monoxide if petrol doesn’t burn properly. 2) A catalytic converter increases the rate at which carbon monoxide and unburnt fuel in exhaust gases react with oxygen to produce carbon dioxide and water. 3) The catalyst has a large surface area and works best at high temperatures to increase the rate of reaction.
More collisions increases the
Rate of reaction!
Higher temperature increases
Collisions!
Higher concentration of pressure increases
Collisions!
Larger surface area increases
Collisions!
Catalyst increases the number of
SUCCESSFUL collisions!
Faster collisions increase the
Rate of reaction! you can only do this by increasing the temperature.
Energy must be supplied to break existing bonds - so breaking bonds is an ______________ process.
Endothermic!