Rates of Reaction
Reactions
Reactions can only occur when two different particles come together. The theory for the way the reaction occurs is called The Collision Theory.
The collision theory states that that the different particles need to collide with each other in order to react. However, they do not react if they collide without sufficient energy, and therefore the more energy a particle has, the more likely it is to react. The activation energy is the minimum amount of energy required by a particle in order to react. When a rate of reaction is improved, the likelihood of the collision of particles is higher and the energy at which they collide is increased.
The importance of rates of reaction
The rate of a reaction is the speed at which this reaction occurs. In different reactions, the rates are different. The two extremes are iron rusting - extremely slow - and an explosion - so fast you cannot tell what's going on!
In our body, there are plenty of reactions taking place every second, in every cell, in order to provide the body with its requirements. These reactions must occur at a certain speed so that the body runs in a smooth manner; the reactions are timed perfectly with the environment in the body.
The rate is very important, and not only in the body. When scientists perform reactions in a lab, they cannot allow the reaction to take very long.
When chemicals and medicine is made in an industry, the aim is to make money. If the reactions take too long, the money is not made as fast as it should be. Also if there is a crisis and medicine is urgently needed, then the reactions would have to be significantly speeded up.
This tells us the importance of the speed of a reaction, and the rates of reaction.
...
This is a preview of the whole essay
The rate is very important, and not only in the body. When scientists perform reactions in a lab, they cannot allow the reaction to take very long.
When chemicals and medicine is made in an industry, the aim is to make money. If the reactions take too long, the money is not made as fast as it should be. Also if there is a crisis and medicine is urgently needed, then the reactions would have to be significantly speeded up.
This tells us the importance of the speed of a reaction, and the rates of reaction.
How are Rates of Reactions Measured?
In order to change the rate at which a reaction occurs we first must measure the current rate and the rate after we have improved the conditions, in an attempt to speed up or slow down the reaction.
In a reaction, reactants are used up and products are formed. It is by observing the speed at which this occurs that we measure the rate of reaction of a reaction. We can observe either of these.
There are many ways in which we can observe this:
* In a reaction where gas is a product, the reaction can be weighed and kept on a weighing scale, in order to observe the change in weight as the reaction proceeds. As the gas is given off, there is a decrease in weight which can be recorded, and we can then see the pace at which the weight was given off.
* When an insoluble solution is a product in a reaction, the liquid in which the reaction occurs becomes opaque, because the solid is now present. In this case the reaction can be measured by placing the beaker/flask over a mark and timing how long it takes until the mark is no longer visible through the liquid.
* In a reaction where a gas is actually given off, we can measure the amount of gas given off in order to measure the rate of the reaction. This can be done by connecting the flask to a gas syringe and measuring the increase in volume, timed.
What affects the rate of reaction?
To increase the rate of reaction in a reaction we must understand the factors which affect it. The rate of a reaction is very variable, and there are three main factors which affect it:
. Temperature
2. Concentration/Pressure
3. Surface area
Temperature
Increasing the temperature around a reaction speeds up the reaction. This is because the increase in temperature has two affects on the reactants which both add up to speeding it up. Firstly, the energy in the particles is increased, so when it collides it is a lot more likely to cause a reaction.
Secondly, the energy in the particle causes them to move around much more, which makes it significantly more likely that there are many more collisions.
Concentration/pressure
In a reaction the particle have to collide; The Collision theory. The more this collision occurs, and the faster it happens, the faster the rate of reaction. In a reaction one of the easiest ways of speeding up a reaction is by increasing the concentrations of the reactants. This speeds up the reaction because there are more particles to collide with each other, and therefore it is more likely that the reaction is completed faster.
A good example of this is acid rain. Many building in the world are made of calcium carbonate in the form of limestone or marble. They have lasted for centuries and only react slightly and slowly with the acid rain. In the last fifty years these same buildings have been crumbling at a must faster rate, because the concentration of the acid in rain has significantly increased, and this causes the rate of reaction to increase.
Surface area
A reaction can take place a lot easier if more of the reactant is exposed. When there is a large lump of a reactant, the inside of it cannot react until the outside has been completed. If the lump was divided then it could be done at the same time, and the reaction would finish faster. This is why we chew our food, and why when cooking, food is chopped up.
This diagram explains how the reactions take place.
In the bigger cube, the volume = 64cm?, and in the smaller cube, volume = 8cm?. 8 small cube can fit into one large cube. For a large cube the surface area = 96cm?. For 8 small cubes surface area = cm?.
