The Effect of Concentrations on the Rate of Reaction

The Effect of Concentrations on the Rate of Reaction
Introduction: In this experiment we are going to be looking at how hcl (hydrochloric acid) and Sodium Thiosulphate affect the rate of a reaction. We will mix the two things together so a precipitate of sulphur will be made. There are many ways in which you could increase the speed of a reaction, for this experiment we will be changing the concentration; to see how that affects the speed of a reaction. There are many other ways to; you could increase the temperature of the substance, increasing the pressure of gas, increasing the surface area of a solid and by using a catalyst. During a reaction where the temperature is constant, the concentration of the reactants decreases and so the rate gradually slows down. For an endothermic reaction increasing the temperature may produce large increases in the rate of reaction. A 10?C rise can double the rate while a 40?C rise can produce a 50 to 100 increase in the rate. The collision theory explains these effects on a gas, liquid and solid.
The theory explains how chemical reactions occur and why rates of reactions differ. In each reaction the particles are constantly moving, therefore when they collide they transfer energy; this means particles are constantly transferring energy between each other. The speed at which a chemical reaction proceeds is usually expressed in terms of concentration (usually in moles per litre), or unit time. If a collision causes a chemical change it is called a fruitful collision. When a reaction does take place, only a certain fraction of the total collisions cause a chemical change, they are called successful collisions. [image] The diagram above shows what a fruitful collision and an unfruitful collision looks like. When reacting two substances, there will be collision within particles in the substance. For a chemical reaction to occur, particles have to hit each other. Particles in a substance can either be an atom, molecule or even an ion. For a reaction to take place, a minimum amount of energy is required. If the colliding particles have less then this minimum energy, the reaction will not occur. They will just bounce of each other and no reaction will take place. This minimum energy is known as activation energy. Fast moving particles have more energy in them; therefore they are more likely to react with each other. To speed up the movement of particles you can heat up the substances that you are trying to react, in this case hcl. Another way to increase the speed of a reaction is to increase the concentration. Increasing the concentration in a solution, will mean that there will be a larger volume, meaning that there will be more particles per dm3 of that substance. As there are more particles, they will be closer to each other. This means that particles collide more frequently with each other and then the rate of a reaction increases. In the reaction of hcl and sodium thiosulphate, increasing the concentration of the hcl substance it means there will be less time before the cross can no longer been seen. Another way to speed up the reaction is to use a catalyst. When a catalyst undergoes collision with the reactant molecules, less energy is required for the chemical change to take place, and hence more collisions have sufficient energy for reaction to occur. The reaction rate therefore increases. Prediction: I think that, as I increase the concentration of hcl the rate of reaction will also increase. This is because there is a more concentration meaning that there are more particles, which are close together and will collide with each other faster. However when I decrease the concentration of hcl the rate of reaction will also be slower. This is because there are fewer particles in the concentration, and they are spaced out more. Therefore it will take them longer to collide with each other. On the whole the larger the amount of hcl the faster the reaction takes place, meaning the quicker the cross will fade. Apparatus: 1. 1 stop clock, 2. 1 thermometer, 3. 1 distilled water bottle, 4. 1m hcl 5. 1 × 10ml measuring cylinder, 6. 1 × 100 measuring cylinder, 7. 1 × 250 conical flask, 8. 5 test tubes, 9. 1 card with black cross, 10. goggles, 11. Spoon, 12. Pen, 13. Test tube rack, 14. 0.15m sodium thiosulphate. Diagram: Method: 1. Firstly collect all equipment, 2. On the paper, draw a black cross, 3. measure out 50cm of 1.0m hcl in a measuring cylinder, 4. measure 50cm sodium thiosulphate in a measuring cylinder, 5. put the conical flask on the paper marked with a cross, 6. pour both the acid and the sodium thiosulphate into the conical flask, 7. mix the chemicals, 8. start stop clock when chemical have been put into the conical flask, 9. keep looking down the conical flask, until you can no longer see the cross, 10. stop the stop clock, 11. write results into your results table, 12. repeat experiment in the same way for all other concentrations of hcl (1.0m, 0.8m, 0.6m, 0.4m, 0.2m) 13. repeat whole experiment for each of the concentrations again, 14. Clean up and pack the equipment away. Safety:
Keep goggles on at all times during the experiment,
Avoid letting chemical touch skin,
Don?t run around the lab while experiments are taking place,
Keep equipment at the centre of a table, to avoid any accidents
taking place,
Work as a group to avoid any spillages.
Fair Test: To make this experiment fair I will keep the following things the same:
Temperature,
Amount of stirs,
Volume of concentration.
Results: Concentration of sodium thiosulphate (M) Time for cross to disappear(seconds) Average time taken for cross to disappear (seconds) Rate of reaction 1/time (s-2) 1.0m 00.40.80 00.40.12 2.4925 1.0m R 00.39.44 0.8m 00.41.65 00.42.02 2.3798 0.8m R 00.42.38 0.6m 00.48.02 00.48.05 2.0811 0.6m R 00.48.07 0.4m 00.58.50 00.58.55 1.7079 0.4m R 00.58.59 0.2m 01.32.61 01.31.59 (91.59) 1.0918 0.2m R 01.30.61 Conclusion: After doing this project I found out that when I increased the concentration of hcl the time taken for the reaction decreased and the rate of reaction decreased to. When the hcl concentration was lower the reaction was slower as it took longer for the black cross to disappear. At 0.2m the reaction took 91.59 seconds on average but the same reaction for 1.0m took 40.12 seconds on average which is less than half the time. The reason for that is there is more collision in the 1.0m than the 0.2m. Meaning the time will decrease. The results corresponded with my prediction.

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