The kinetic theory Essay Example for Free

The kinetic theory Essay In this investigation, I will be studying the factors that affect the rate of reaction. In this case, the reaction between hydrochloric acid and sodium thiosulphate. Na2S2O3 (aq)+ 2HCl(aq) 2NaCl(aq)+S(s)+SO2(g) When hydrochloric acid is added to sodium thiosulphate, the chemicals react giving solid sulphur as one of the products. This is a precipitation reaction. By watching the speed at which the sulphur has formed, we can find out the rate of reaction. A cross can be marked on a piece of paper, and a flask of sodium thiosulphate can be placed on top. By adding hydrochloric acid to the sodium thiosulphate, we can time how long it takes for the view of the cross to become obscured by the sulphur. We can then find out the rate of the reaction. What is Rate? Chemical reactions can be seen everywhere, whether an explosion, which is extremely fast, to something very slow, like the rusting of a metal. It is not enough just to know whether something is fast or slow however. Rate is a measure of the change that happens in a single unit of time. For example, if a car travels 40 km in half an hour, it is travelling at 80 km/h. For a chemical reaction to take place, some bonds in the reactants must be broken. The colliding particles must have enough energy to break these bonds. This minimum amount of energy is called the activation energy. Only the very fastest moving particles have enough energy to break bonds. In gases, liquids and in solution, the particles move at a range of speeds. Some are moving very slowly and others are moving very fast. To react, particles must collide with enough energy and in the correct orientation for bonds to be broken. If there is not enough kinetic energy, the particles barely touch, and the reaction does not happen. If the kinetic energy of the particles is just right, they hit each other and form new bonds. For a reaction to take place, the alignment of the molecules must also be correct. If two or more molecules collide, but are not orientated correctly, a reaction cannot take place. Variables Concentration of Thio If the concentration of thio is increased, the rate of reaction is also increased. This is because in dilute acid, there are not many acid particles. This means there is a more remote chance of an acid particle, hitting a sodium thiosulphate particle. In a more concentrated acid, there are more acid particles. There is now more chance of an acid particle colliding with a sodium thiosulphate particle, and so more chance of a collision. I have chosen this variable to use, as it will be possible to get a wide range of results with relative ease. I also feel that there will be a significant enough range of values in the results to make an effective graph. I could change this variable by adding water to the sodium thiosulphate to make it less concentrated. I will need to keep the volume constant throughout the experiment, so I could, for example use 40 cm3 of sodium thiosulphate and 10 cm3 of water, and then 30/20 etc. Temperature At low temperatures, particles of reacting substances do not have much energy. However, when the substances are heated, the particles take in energy. This causes them to move faster and collide more often. The collisions have more energy; so more collisions are successful. Therefore, the rate of reaction increases. This is called the kinetic theory. A reaction goes approximately twice as fast when the temperature is increased by 10 degrees. This is why it is important to keep this variable constant . To do this; I will need to do the experiment on the same day if possible. This ensures that the differences in room temperature, however small, do not affect the rate of reaction. Surface Area In a reaction containing a solid, its surface area has a large effect on the rate of reaction. If the surface area of the solid is small, the acid particles can only collide with the atoms in the outer layer of the solid. But if the solid has a large surface area, much more of the atoms are exposed, so there is a greater chance of one of these atoms colliding with an acid particle, and increasing the rate of reaction. However, in my experiment, I will not be using any solids, so this variable will not affect my experiment. Use of a Catalyst A catalyst is a substance that changes the rate of a chemical reaction but remains chemically unchanged itself. It does this by lowering the activation energy; this is the amount of energy needed in order to achieve a successful collision.