in today's video we're going to look at the factors that affect the rate of chemical reactions so temperature concentration or pressure surface area and the presence or absence of a catalyst before we can understand how these factors affect the rate though we need to cover the theory behind reactions which is known as collision theory this states that in order for particles to react they have to collide with each other with sufficient energy which we call the activation energy and if they collide with less energy than this then nothing will happen they'll just bounce apart again so if we were to think about an entire reaction which will involve tons of particles then the rate at any particular point is going to depend on two main things the most obvious is the amount of energy that the particles have the more energy they have the more energy they can transfer during the collision and so the more likely they are to surpass that minimum activation energy the other important thing is the frequency of the collisions which just means how often the particles collide with each other so even though not all collisions are successful because the particles involved don't always reach activation energy the more often they collide the more successful collisions they'll be overall now whenever you think about how these four factors affect the rate of reaction you always want to think in terms of how they affect the amount of energy that the particles have and the frequency of the collisions as increasing either of these will increase the rate of reaction by increasing the number of successful collisions let's start with temperature as the temperature of a reaction increases the particles gain more energy which means that they move faster and because they're moving faster they'll collide more frequently they'll also collide with more energy each time so are more likely to exceed the activation energy so overall there will be a higher rate of successful collisions and thus a higher rate of reaction now concentration and pressure are normally considered as a single factor because they both refer to how many particles there are per unit of volume it's just that concentration generally refers to solutions and pressure refers to gases when either of these is increased it means that there'll be more particles per unit of volume which makes the collisions more frequent and so increases the rate of reaction just like concentration and pressure a higher surface area will also increase the rate of reaction for example if we wanted to react three grams of magnesium with an acid we could use a solid block of magnesium small chunks of magnesium or powder as all of these have the same mass and volume the powdered form would have the highest surface area to volume ratio and so we'll have a much higher area over which collisions with the other reactants in this case the acid could take place meaning that the frequency of the equations would be higher leading to a higher rate of reaction the last factor that we need to cover is the presence of a catalyst catalysts are substances that speed up a reaction without being used up in the reaction themselves so we don't include them in the reaction equation as they're not reactants or products to understand how they work we can use a reaction profile which shows the change in their chemicals energy during a reaction now this distance between the reactants energy level and the very top of the curve is the activation energy which remember is the energy that the collisions have to have before they can react successfully what a catalyst does is lowers this activation energy by providing an alternative reaction pathway and this means that there'll be a higher proportion of successful collisions the word catalyst is actually a pretty broad term and a whole range of different substances can act as catalysts in different situations one of the most common sources of catalysts though are the transition metals like cobalt and nickel and if you do biology you'll have come across them in the form of enzymes which are just catalysts made by living organisms anyway that's all for this video so hope you enjoyed it and we'll see you next time