Factors that affect rates of reaction: The rate of a reaction depends on mainly 6 things; temperature, concentration, if catalysts are present, volume of the liquid, size of container and size of particles. The rates of chemical reactions vary greatly, for example rusting of iron is a very slow process although explosions are extremely fast reactions. For a chemical reaction to take place, the particles of the reactants must collide with each other and the collisions must have enough energy to break reactant bonds and form products. The higher the number of successful collisions, the faster the rate of a reaction. This is called the Collision Theory. Here are factors, which affect rates of reactions;
Temperature: If reacting substances are heated, the rate of a reaction will rise. This is because the heat gives the particles in the substances more energy to move around so that there will be more successful collisions. The heat energy makes the particles move faster, which will increase the chances of collision because when they move slowly, particles can just bounce off each other. Cooling of the reactants in the substance causes the opposite affects of heating.
Concentration: If a solution is highly concentrated, then there are more particles in the reactant to collide with. Therefore, there will be more successful collisions, meaning that the rate of the reaction will be fast. If the same volume of solvents were not kept the same, this would change the concentration, which would make the experiment unfair.
Size of particles: If a solid reactant is small in size, then this means that there is a larger surface area exposed for the particles in the solution to collide with. Therefore, there will be more successful collisions, meaning that the rate of the reaction will be fast.
Catalysts: A catalyst gives the reacting particles a surface area to attach to, so they are able to collide more. This means that reactants don’t need as much energy to collide with particles as they are being helped by the catalyst. They make the reactions faster but remain chemically unchanged themselves. Catalysts are important in industry as they allow manufacturers to produce products more rapidly. There are two types of catalysts, homogenous and heterogeneous. A homogenous catalyst is one that is in the same physical state as the reactant. A heterogeneous catalyst involves two physical states, such as a solid catalyst affecting a liquid reactant.
Size of container: As liquids take the shape of their container, this will affect the rate of reaction. If a container is extremely large, the reactant particles will be extremely spaced out in the solvent and will have less chance of colliding with another particle as they might not have enough energy to travel that far. In a small container, the reactant particles would be close together and therefore would find it easy to collide with another particle.
Apparatus:
Conical Flask
Magnesium
Sulphuric Acid
Water
Measuring Tube (25ml)
Rubber Bung connected with gas tube
Water trough
Timer
Drawing of Set up:
Results:
This table shows the time taken for hydrogen, being given off from the reactants, to fill a 25ml measuring tube.
Conclusion: From the results I have obtained, I think that they are accurate because I repeated the experiment twice and the results were extremely similar. Before drawing the graph, I had planned to use a line of best fit to work out the gradient and therefore find out the rate of reaction but the graphs didn’t lend themselves to having lines of best fits, but rather curves of best fits. I then used this curve of best fit to draw tangents off the line to work out the gradients. For experiment 1 these were the gradients I found:
The gradients for both experiments were quite similar which proves that my results were accurate. These gradients show the average time it took to react with a certain molar.
I think that the results for 0.2 molar of sulphuric acid was a weird result because it didn’t go in the same pattern as all the other results, but I think it is still correct as it was nearly the same for both experiments. The pattern in the results was when you increased the amount of sulphuric acid by 20ml and reduce the amount of water by 20ml, the time taken to react is around 5 seconds less, but this pattern does not include the weird result for 0.2 molar of sulphuric acid.
My prediction was right, the higher the amount of concentration of sulphuric acid to water, the faster the rate of reaction between magnesium. This was because there were more sulphuric acid particles for the magnesium particles to collide with. So I believe that this statement is true;
“The higher the concentration of a reactant, the faster the reaction will take place.” The results support my prediction because as more water was put in the solution, the slower the reaction took place. I was able to find out the equation of what happened in my experiment.
Mg+ H2SO4 Mg SO4+2H
Magnesium + Sulphuric Acid Magnesium Sulphate + Hydrogen
Evaluation: I think my experiment went well as my results were accurate and I was able to find the answer to my aim. I know that my results were accurate because I did the experiment twice and both sets of results were really similar.
I think the only weird results I got were for 0.2 molar of sulphuric acid. I think that the concentration of 0.2 molar of sulphuric acid, took such a long time to fill the measuring tube with hydrogen compared with the other molars, was because the amount of water was so high, it was hard for the sulphuric acid particles to collide with the magnesium particles.
I think my method was good as it was able to let me find my answer to how concentration affects the rate of a reaction, accurately. Although, I would have improved the experiment by using a syringe to measure the amount of hydrogen because it would have been more accurate than the measuring tube. I also think that to get an even more accurate answer to my aim, I could have done the experiment again but using a different solvent instead of sulphuric acid such as hydrochloric acid. This would then mean that I would be able to find out if concentration affects rates of reaction even if I use a different solvent.
If I wanted to take my investigation further, I would put a thermometer in the conical flask to find out if concentration also affects the temperature of the solution. I would also further my investigation by putting the flask on an electric weighing scale to see if concentration also affects the mass of the solution, as it might get heavier or lighter.