A reaction takes place when two different molecules collide; this is only possible when the particles have enough kinetic energy. This energy requirement is called the activation energy (AE). The rate of a reaction can be altered by the following: – – Temperature – Catalyst – Concentration – Surface Area Below shows a graph, this illustrates the effect which the above have on a reaction:- We can measure the rate of a reaction by doing the following: – Measuring how long it takes for a certain volume of CO2 takes to be produced. Timing how long it takes until the reaction stops.
Measuring the loss in mass of the reactant over time. Aim To investigate the effect that concentration has on the rate of a reaction. Scientific Theory The rate of a reaction can be affected by 4 things (stated above) below show what these are and how they alter the rate of a reaction. Temperature – The higher the temperature the greater the amount of kinetic (movement) energy is available. Therefore the more energy that the particles have the faster the molecules move and the greater the chance that they will collide with the reactant.
This means that the rate of the reaction is increased. A lower temperature would mean less kinetic energy resulting in a slower reaction. Below shows a graph demonstrating the effect this has: – Concentration – The higher the concentration means the more molecules there are present in a certain volume with the minimum amount of energy for the reaction to begin. If there is a high concentration there will be more molecules present in a smaller area. This results in the probability that particles will collide with the reactant increases.
A weaker concentration would mean that there are fewer molecules available to react resulting in a slower reaction. Below shows an example of this: – Catalyst – A catalyst alters the rate of a reaction (taking no part, remaining unchanged) by changing the activation energy level (the amount of energy needed for the reaction to take place) this provides an alternative route for the reaction with a lower activation energy. A positive catalyst speeds up the rate of a reaction by lowering the activation energy; therefore more particles will have the amount of energy needed for the reaction to take place.
A negative catalyst slows down the rate of a reaction by increasing the activation energy levels resulting in fewer molecules having the minimum energy to collide causing the rate of a reaction to decrease. Below shows a graph showing this: – Surface area – The greater the surface area visible, the more molecules on the solid there are available to react, therefore the chance of particles colliding with enough kinetic energy is increased and so the rate of a reaction is increased. During this experiment I will be looking at what effect the concentration of an acid has on the rate of a reaction.
I have chosen concentration because it is one of the easiest to monitor. I will ensure that I keep the other variables constant. I conducted a pilot experiment to gather preliminary results and to ensure that the decisions I make for the actual experiment are wise and will help me gather a reliable set of results, During the experiment I used the following concentrations of Hydrochloric acid: – – 0. 1 m – 0. 5 m – 1. 0 m – 1. 5 m And used magnesium with length of 2 cm My results were as follows Concentration Test 1 Test 2 Test 3 Average 0.
1 Over 10 minutes Over 10 minutes Over 10 minutes Over 10 minutes 0. 5 350 secs375 secs 320secs 348 secs 1. 0 62 secs 71 secs 73 secs 69 secs 1. 5 31 secs 29 secs 34 secs 31 secs Based on my preliminary results I have found the following helpful towards my actual experiment: – I will not be using the concentration of 0. 1 moles because it was very slow at reacting and so I will now be starting at 0. 5 moles. 2 cm of magnesium has a large surface area and so takes a long time to react. I will use a 5th concentration to give myself a broader basis to back up my prediction.
I will record all times to . 1 of a second Key Factors Here is a list of variables that can affect the experiment: – The length of the reactant (magnesium) – The larger the surface area the longer it will take to react The concentration of acid – The higher the concentration the denser the acid particles are and so the greater the chance that the acid particles and the magnesium particles will collide.
The surrounding temperature and temperature of the solution – If the temperature is high then this large amount of thermal energy will convert into a large amount of kinetic energy, the acid molecules will travel faster and so they will collide with the magnesium particles more often. The reaction therefore will occur much faster.