This frequently causes problems! The graph below show typical changes in concentration or amount of moles remaining of a reactant with time, for zero, 1st and 2nd order.
The reciprocal of the reaction time can be taken as a measure of the speed of the reaction at that particular temperature. More details of laboratory investigations 'labs' involving 'rates of reaction' i. Why does a reaction go faster at a higher temperature? The greater the temperature of the reactants, the greater the average kinetic energy of the particles.
Therefore, the more chance of a successful more energetic 'fruitful' collision between two particles with sufficient combined kinetic energy to overcome the activation energy barrier, break bonds and form the products. The frequency of collision increases too, but this is the lesser of the two factors which both contribute to an increased rate of reaction on raising the temperature.
When gases or liquids are heated the particles gain kinetic energy and on average move faster see diagrams below. The increased speed increases the chance frequency of collision between reactant molecules and the rate of reaction increases.
BUT this is NOT the main reason for the increased reaction speed, so be careful in your theory explanations if investigating the effect of temperature, so read on after the pictures! The more important factor is the kinetic energy of the particles and therefore the higher energy collisions when the temperature is raised.
Most molecular collisions do not result in chemical change. Going up and to the top 'hump' represents bond breaking on reacting particle collision. The purple arrow up represents this minimum energy needed to break bonds to initiate the reaction, that is the activation energy.
Going down the other side represents the new bonds formed in the reaction products. The red arrow down represents the energy released - exothermic reaction.
It does not matter whether the reaction is an exothermic or an endothermic in terms of energy change, its the activation energy which is the most important factor in terms of temperature and its effect on reaction speed. Now heated molecules have a greater average kinetic energy, and so at higher temperatures, a greater proportion of them have the required activation energy to react i.
This means that the increased chance of 'fruitful' higher energy collision greatly increases the speed of the reaction, depending on the fraction of molecules with enough energy to react. For this reason, generally speaking, and in the absence of catalysts or extra energy input, a low activation energy reaction is likely to be fast and a high activation energy reaction much slower, reflecting the trend that the lower the energy barrier to a reaction, the more molecules are likely to have sufficient energy to react on collision.
See also graphs 4. BUT, the energy bill should not be economically demanding, the speed of reaction at higher temperature must be under control and not too fast to be dangerous, if the reaction is exothermic and an equilibrium is formed, operating at too high a temperature might significantly reduce the yield.
The minimum energy needed for reaction, the activation energy to break bonds on collisionstays the same on increasing temperature. However, the average increase in particle kinetic energy caused by the absorbed heat means that a much greater proportion of the reactant molecules now has the minimum or activation energy to react.
So, at a higher temperature, there are more particles with the higher kinetic energies. Therefore there will be more particles colliding with enough energy to overcome the threshold activation energy.
It is this increased chance of a 'successful' or 'fruitful' higher energy collision leading to product formation, that is the major factor, and this effect increases more than the increased frequency of particle collision, for a similar rise in temperature.
There is also the Arrhenius Equation relating rate of reaction and temperature - but this involves advanced level mathematics.Seneca helps you to learn 2x faster at GCSE, A Level and KS3 for free.
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