rates of reaction

rate of reaction: how quickly/slowly a reaction takes place.

we can monitor reaction rates through:

change in mass

change in volume

for example, when marble (calcium carbonate) reacts with hydrochloric acid.

CaO3 + 2HCl ---> CaCl2 + CO2 + H2O

the law of conservation of mass still applies here,but carbon dioxide (a gas) is formed.this gas can escape and affect the mass of the product.you can measure the volume of carbon dioxide produced to show 'how much' reaction has taken place.the more carbon dioxide there is, the more reaction has taken place.

activation energy: minimum energy needed to break the bonds (start a reaction).

for chemical reactions to take place, the reactant particles must collide with enough energy to react.

reaction rates increase when..

increase the force of collision

increase the frequency of collisions (how many collisions)

reactions that release energy are called exothermic.these kinds f reactions continue unless stopped as this release of energy causes another reaction to take place , like dominos. e.g a fire

temperature increases the rate of reaction,as a higher temperature means more kenetic energy, which leads to more collisions.

pressure increases the rate of reaction, beacuse a higher pressure leads to more collisions (as there is less space)

concentration increases the rate of reaction, because if there are more particles,there is more chance of them colliding.

surface area increases the rate of reaction, as is there is more area to collide with, there is a higher chance of collision. for example, there is a better chance for a tennis ball to hit a big racket than a small one.

reactions between gases are slower than reactions between liquids of the same temperature, because particles in a liquid are closer than particles in a gas, so they have a better chance of colliding.                                                                               

catalyst: speed up rates of reaction without being use up.e.g iron catalyst.

manufacturers use catalysts for many reasons..

to lower the activation energy (this leads to a greater yield)

makes the reaction faster

saves energy, which saves money.

in a catalyctic coverter, the catalyst used is usually platinum or palladium. they can be used even though they are expensive, as only a small amount is needed.this small amount is spread over a honeycomb structure to create a very lerge surface area.this increases the rate of reaction.

enzymes: biological catalysts.speed up the rate of reactions.e.g pepsin breaks proteins down into amino acids.

an enzymes active site can become denatured.this may be the result of...

high temperatures

the wrong PH

however, a chemical catalyst can never become denatured.

denatured: when the substrate can not fit into the active site(lock and key diagram)