Chemistry Rate of Reaction

GCSE Science Chemistry Coursework

What Affects the Rate of Reaction?

In this coursework I will be answering the above question; this will be done from an investigation into an experiment. In this experiment I will conduct various pre-test so I know what component I will use in my main experiment to get the best and fairest results.

A reaction is a chemical process that occurs between two elements to produce a bi product like thermal energy, light, kinetic energy or another element or a compound

What are the main factors that affect the rate of reaction?

The speed that the reaction takes place is inversely proportional to the time taken for the reaction to finish.

There are two main types of reactions that are most common in the world around us, exothermic reaction one that gives off heat due to bonds being broken, the other is an endothermic reaction, where heat is being taken in due to the construction of new bonds.

Size of particle

The size of the particles that are going to be reacted has a great impact on how long the reaction takes place for. If particles are small there is a larger surface area for the substance to react on thus increasing the probability of a collision, increasing the rate of reaction and decreasing the time of the reaction.

Small surface area large surface area

Another thing that affects the rate of reaction is the atomic structure of the chemical. If we are dealing with elements the electrons on the outer shell determine how well they react, e.g. if the outer shell is full of electrons like neon it has very little intentions to react, but if there is only one electron in the outer shell or seven these elements will be highly reactive. Either to gain or lose an electron.

Pressure

If pressure is exerted onto the reaction it can have different effects. If there is an increase in pressure on the reactant this means that it will result in a increase in the rate of reaction due to molecules of each substance are packed closer together, increasing the chance of a collision The smaller the volume a given amount of gas is squeezed into, the greater the pressure the gas or liquid exerts on the walls of its container. A decrease in pressure results in the rate of reaction slowing down due to particles is further apart and kinetic energy is lost so they slow down and collides with less force.

Concentration.

In this experiment the concentration can be altered in various ways. Increasing the strength of the acid, making it stronger or weaker by adding more parts of acid per water. Also I can increase the amount of the hydrochloric acid I put in, 10ml to 20ml doing this increases the chances of molecules colliding due to there is more chance of a collision, however As a reaction proceeds, the concentration of the reactants usually decreases as they are used up. The rate of reaction will, therefore, decrease as well. If I do double the amount of hydrochloric acid there will be a twice as likely chance of a successful collision taking place. N.B if I have 100 moles of hydrochloric acid and 10 successfully collide, 200 moles I would expect 20 to collide as there is a twice as likely chance.

Catalyst

A catalyst is a substance that speeds up the rate of a chemical reaction, without the catalyst itself being processed into the reaction, however not all catalyst speed up the rate of reaction some slow down the reaction this is called a negative catalyst. A positive catalyst speed up an reaction by providing a surface area for the substance to react on increasing the chances of a collision between the substances, this is very useful because it lowers the activation energy of the initial reaction to get started.

Temperature

The higher the temperature of the reactant the fast the reaction will occur. This is because heat gives molecules more kinetic energy so they whiz around more increasing the chances of a collision happening as they have more kinetic energy so if the solution is heated from 20 degrees to 40 degrees I believe they will be as twice as fast and twice as many collisions will take place than at 20 degrees. Also if a collision takes place it does not guarantee a reaction taking place, there is a minimal amount of energy needed called the activation energy, before a reaction can take place. However as the particles are heated up their energy potential they have is increased, so if they collide they do it with a greater force so there is a greater success of a reaction taking place.

My investigation Prediction

In this coursework I will be investigating how sodium thiosulphate reacts with hydrochloric acid. I predict that a decrease in the concentration of the reactant will result into a longer waiting time for the reaction to complete. The speed of the reaction is inversely proportional to the time of the reaction taking place. This is because as there is less hydrochloric particle in the solution half the number of collisions will take place between it and the sodium thiosulphate, thus decreasing the reaction time. The same theory is applied if the concentration is doubled, more sodium thiosulphate acid for the hydrochloric to react with , making more successful collision take place and more successful breaking of bond this reduced the time of the reaction to complete. When the concentration of sodium thiosulphate is increased there is twice as much particle for the hydrochloric acid to react with, so there is a twice as much chance of a successful collision taking place between the two substances. So if the number of successful collision taking place double so should rate of the Bi product. If sodium thiosulphate is doubled so should the rate of the reaction.

Na2S2O3(aq) + 2HCl(aq) ==> 2NaCl(aq) + SO2(aq) + H2O(l) + S(s)

Fair test

Before conducting the practical I first must make sure that, it will be a fair test

This will be achieved by,

Carrying