The rate of reaction tells us how quickly a chemical reaction takes place-i. e. , how long it is before the reactants are fully reacted, and how much product is produced in a certain period of time. The rate of reaction is affected by the reactivity of the substances; for example, potassium is more reactive than iron. There are various different rates of reaction that can be measured: (1) Forward Rate: The rate of the forward reaction when reactants become products. (2) Reverse Rate: The rate of the reverse reaction when products recombine to become reactants.
(3) Net Rate: The forward rate minus the reverse rate. (4) Average Rate: The speed of the entire reaction from start to finish. (5) Instantaneous Rate: The speed of the reaction at one moment in time. During a chemical reaction, the bonds between the atoms of substances are broken and the atoms rearrange themselves to form new bonds. The Law of Conservation of Mass states that mass cannot be created or destroyed during a chemical reaction; atoms may rearrange, but after the chemical reaction has taken place, there is still the same number of atoms, and therefore the same amount of matter.
The Rate of Reaction is just to do with how quickly this takes place. There are many variables which affect the rate of reaction; in this experiment, I will be investigating the effect that concentration has on the rate of a reaction. Aim In this investigation, I hope to discover the effect that concentration of Hydrochloric acid has on the rate of reaction with marble chips (Calcium Carbonate). Planning The reaction I will be investigating is between calcium carbonate (CaCO3) (in the form of marble chips) and hydrochloric acid (HCl). Hydrochloric Acid + Calcium Carbonate
–> calcium chloride + carbon dioxide + water Hcl(aq) + CaCO3(s) –> CaCl2(aq) + CO2(g) + H2O(l) The best way in which to measure the rate of reaction is to measure the amount of product formed within a set period of time; the more of the product made in the time space, the higher the rate of reaction. In this case, the product I will be measuring is Carbon dioxide (CO2) I will do this by reacting different concentrations of hydrochloric acid with the same mass of marble chips, and measuring how much gas is given off over a period of time.
As the aim is to find out how concentration affects rate of reaction, the only variable I need to change is concentration; the others must be kept constant in order for it to be a fair test (see ‘Fair Test’). Preliminary Testing It was necessary to carry out some preliminary tests in order to decide the range of readings and quantities of reactants to use. The acid is a 2M solution and will be diluted using distilled water; I needed to decide how much liquid to use overall, and what quantity of marble chips to use.
In order to discover this, I set up the experiment in the way I intend to do it-see Method-and first of all carried out the experiment with 100 ml of acid and 10g of marble chips. With these quantities, I found that the reaction took place extremely quickly, and the amount of product produced was soon off the scale. I then carried out the experiment with 50 ml of acid, and 5g of marble chips. Again, the amount of product was off the scale-it was the same when I carried out the experiment with 50 ml of acid and 2. 5g of marble chips. With my preliminary testing in mind, I have decided to use 50 ml of liquid overall, and 1g of marble chips.
Method EQUIPMENT LIST Measuring Cylinder DIAGRAM STEP-BY-STEP METHOD Set up the gas syringe in the clamp, horizontally. We do this because if the syringe was to be held in someone’s hand, their body heat would affect the temperature. Measure the appropriate amount of acid and distilled water and place in conical flask.Connect the end of the connecting tube to the gas syringe Measure 1g of medium-sized marble chips. Add chips to the flask. Put the stopper in the flask and start the stop-clock.0
Record the amount of gas in the syringe at 10 second intervals for 3 minutes. I will do 11 different experiments, including the control: 1. 50 ml of distilled water, 0 ml of hydrochloric acid (control) 2. 45 ml of distilled water, 5 ml of hydrochloric acid 3. 40 ml of distilled water, 10 ml of hydrochloric acid 4. 35 ml of distilled water, 15 ml of hydrochloric acid 5. 30 ml of distilled water, 20 ml of hydrochloric acid 6. 25 ml of distilled water, 25 ml of hydrochloric acid 7. 20 ml of distilled water, 30 ml of hydrochloric acid 8. 15 ml of distilled water, 35 ml of hydrochloric acid 9.
10 ml of distilled water, 40 ml of hydrochloric acid 10. 5 ml of distilled water, 45 ml of hydrochloric acid 11. 0 ml of distilled water, 50 ml of hydrochloric acid I have chosen this number of readings because it will enable me to see how reliable the results are by drawing a graph, and also because it covers a wide enough range to allow me to make an educated hypothesis. I will take repeat readings in order to verify reliability; it will be necessary to take the repeat readings by repeating the whole experiment again. I will record the amount of gas given off at 10 second intervals for 3 minutes.
FAIR TEST There are a number of variables other than just concentration which affect the rate of reaction; for this investigation it is vital to keep these variables constant in order to make it a fair test. The only variable which needs to be changed is concentration. For a chemical reaction to take place, the particles of the reactions must collide, and the collision must have enough energy. The minimum energy that the particles need in order to react is called the activation energy. If the particles have less than this amount of energy, they simply bounce off each other and no reaction takes place.
The faster the particles are going, the more energy they have. This is the collision theory. From this we know that the more collisions between particles in a given time, the faster the reaction. The particles in the liquid are moving continuously, thus allowing for collisions with the metal particles. If the collision has enough energy, a chemical reaction will take place between the two particles. The more collisions, and chemical reactions, that take place in a given time, the higher the rate of reaction. Variables that affect the rate of reaction are things that affect the amount of collisions in a given time.
These include surface area, concentration, and temperature. Surface Area As we increase the surface area, we increase the rate of reaction. This is because the only particles which can collide in a reaction, are the particles on the surface of a solid. A larger surface area means that there are more particles exposed, and therefore more collisions can take place per second, increasing the rate of reaction. In this investigation, the size of the marble chips could affect the rate of reaction and stop it from being a fair test. To prevent this, I will select marble chips all of a similar size to use for the investigation.