Temperature's Effect on Rates of Reaction

Temperature's Effect on Rates of Reaction
Aim: In this investigation, I aim to find out how temperature affects the rate of reaction between hydrochloric acid and magnesium ribbon. Introduction: In solids, liquids and in a solution, the particles move constantly but at different speeds to each other. Some particles are moving faster or slower than others are. But for a chemical reaction to occur the bonds in the reactants have to be broken. They are broken by the collisions between particles. The successful collisions are those that have enough energy to break these bonds. This "minimum amount of energy needed to break the bonds" is known as the activation energy. -
As more and more collisions occur, the more successful collisions there are going to be. These successful collisions affect the rate of reaction as in it is increased. So the fewer collisions there between particles the fewer successful collisions there are. This leads to a slower rate of reaction. -????????????????????????????????? When Hydrochloric acid and Magnesium are placed together, a reaction occurs. Here is a word equation for the reaction: [image]Magnesium + Hydrochloric acid Magnesium Chloride + Hydrogen. Here is a balanced symbol equation for the reaction above: [image]Mg + 2HCl MgClâ?? + Hâ?? The reaction between hcl and Mg occurs using the collision theory I explained earlier. However the rate of this reaction is affected by various factors as listed below: Â? Concentration Â? Surface area and particle size Â? Temperature Â? Catalyst I shall now explain how these factors affect the rate of a chemical reaction and particularly the reaction of HCl and Mg. If you increase the concentration of reactants as in HCl this means that there are more particles in the same volume. If there are more particles this means that there will be more collisions between particles. As more collisions happen there obviously will be more successful collisions. This increase in number of successful collisions leads to a quicker rate of reaction. So if the concentration is decreased the number of particles for a given volume decreases too. Fewer particles means that there are fewer collisions. And therefore there would be fewer successful collisions between particles of reactant. Overall this means that there would be a slower rate of reaction. [image] Dilute acid ? few particles Concentrated acid ? many particles Surface area also affects the rate of reaction. Large chips/solids of the Magnesium means that they will have a smaller surface area. A smaller surface reduces the chances of particles at show reacting. So there are fewer particles at show to react. This means that there would be fewer successful collisions and a slower rate of reaction. Whereas if powdered Magnesium was used in the reaction with Hydrochloric acid then the surface area would increase. More surface area means that there are more particles at show to react with. The more particles there are the more collisions between other particles of reactant there are. So there will be more successful collisions and a quicker rate of reaction. When you increase the temperature of a reaction, the rate of a reaction is increased. At high temperatures reactant particles move faster because they have more energy. So with more energy they are moving around a lot more often and colliding with other particles a lot more. More collisions means that there would be more successful collisions. Again successful collisions between particles of reactant mean that there will be a quicker rate of reaction. The opposite would occur if the temperature is decreased. Low temperatures mean that there would be less energy within the particles and these particles would not collide very often. Fewer collisions mean that there would be fewer successful collisions and a slower rate of reaction would happen. [image] Low temperature ? less collisions High temperature ? more collisions Catalysts are often used in reactions but they can slow down and speed up a reaction. But catalyst themselves do not change or are used up in reactions. A ?positive? catalyst speeds up the reaction by breaking more bonds. This then lowers the activation energy needed and so the particles can react with less energy but still have a quicker rate of reaction. A ?negative? catalyst slows down a reaction by increasing the activation energy. So the particles of reactant need more energy to cause successful collisions to occur. This means that there would be a slower rate of reaction. Prediction: -???? Based on my research I predict that the higher the temperature the quicker the rate of reaction. I predict this because higher temperature means that there is more energy in the particles of reaction. More energy means that the particles are moving about constantly and a lot more. More movement of particles means more collision. In addition, frequent collisions means that there are more successful collisions leading to a quicker rate of reaction. -????????????????????????????????? Apparatus: -???- Below are the pieces of apparatus that I shall use to carry out my experiment. -???????????????????????????????- Â? Measuring cylinder (100cm) -????????????- Â? Conical flask -?????? Â? Goggles -??? Â? Stopwatch -???? Â? Hydrochloric acid (HCl) -??????????? Â? Magnesium (Mg) -??????- Â? Thermometer -????? Â? Tripod -??- Â? Bunsen burner -?????? Â? Gauze -?? Â? Laboratory mat -??????- Â? Tongs -?? [image]Diagram: Method: 1. Firstly, I shall set up the apparatus as shown in the diagram. 2. I will measure 50cm of hcl acid and I will transfer this to the conical flask. 3. After that, I shall use tongs and place the magnesium ribbon into the hcl. 4. The first temperature I shall keep the acid at is 20Â?C. 5. As soon as the magnesium is placed, I shall start the stopwatch. 6. I will stop the stopwatch as soon as the reaction has settled and magnesium has stopped reacting. 7. I shall repeat the experiment three times. 8. After repeating the experiment, I shall differ the temperature to 30Â?C and repeat this experiment three times as well. 9. I shall then do the same again but with temperatures of acid at 40Â? C and 50Â?C. 10. I shall then take an average of my results and plot a graph using my results. Fair test: -???- In order to keep my experiment fair I must do the following: -????????????????????????????- Â? Keep the amount of hcl used the same each time. Â? Use the same amount of magnesium each time as well. Â? After each experiment, I will rinse out the apparatus with water. Safety: -?? As well as keeping the experiment fair I also have to make sure it is safe to carry out. To reduce any accidents from occurring I will do the following: -????????????????????????????????? Â? I must wear goggles. Â? I have to place a lab mat under the Bunsen burner, so that the table does not burn or stain. Â? I will make sure that I do not work near a socket when dealing with the chemicals. Â? I will clean the surfaces after use, and if any substances are dropped. Â? I will keep my bags etc. away from the experiment. Table of results: Temperature (Â?C) Experiment no: 20 30 40 50 1 2 mins: 19secs 1min: 11 secs 1min: 6 secs 49 secs 2 2 mins: 20 secs 1 min: 13 secs 1 min: 4 secs 48 secs 3 2 mins: 18secs 1 min: 12 secs 1 min: 5 secs 47 secs Average 2 mins: 19 secs 1 min: 12 secs 1 min: 5 secs 48 secs The times show the rate of reaction. For example, the rate of reaction at 20Â?C for experiment 1 was 2 minutes and 19 seconds. Now using these results I shall plot a graph. Conclusion: After doing my experiment I found out that the increase in temperature means a decrease in temperature. And a decrease in temperature showed that there was an increase in the rate of reaction. -?????????????????????????????????- My graph has a negative gradient and is a curve. As the temperature at the x-axis increases the rate of reaction at the y-axis decreases. So the temperature is inversely proportional to the rate of reaction. -?????????????????????????????????- This shows me that the higher the temperature the quicker the rate of reaction. This is because as I explained in my introduction that higher temperature means that there is more energy in the particles. When these particles have more energy they move around a lot more. This movement means that they collide with other particles. As they are moving around a lot there are many collisions between particles. The increase in collisions means that there obviously will be a quicker rate of reaction. -????????????????????????????????? At 50Â?C the rate of reaction was quickest. This was because the higher temperature meant that the particles had more energy and broke the bonds between particles quicker lowering the activation energy. -?????????????????????????????????- At 20Â?C the temperature was the lowest out of my experiments. My graph shows that the rate of reaction was longest at the lowest temperature. This was because the particles had less energy in them and so they moved around less so there were fewer collisions. And out of those fewer collisions there were fewer successful collisions. That is why at 20Â?C the rate of reaction was longest. I predicted that as the temperature increased the rate of reaction decreased. I predicted correctly as my results show. At 20Â?c of temperature, the rate of reaction was 2 minutes and 20 seconds and this was the longest rate of reaction of the four temperatures. The rate of reaction was slow because the temperature was low. I also predicted that the fastest rate of reaction would be at 50Â?C. I was correct and this was because the temperature was higher. -???????????????????????????????? Evaluation: My graph shows that my results were quite accurate. I know this because three of the four points are on the line of best fit. The fact that I got accurate results was because I followed my method. This helped me to get good results. My table of results have quite good measurements. The three repeats of the same experiments, all are quite similar results. This was because I started and stopped the stopwatch as soon as the experiment started and as soon as it stopped. This was a good idea because I got accurate results. Also I repeated the experiment and this helped me to get good results. The line of best fit on my graph has one result at 40Â?c, quite far off. It is an anomalous result. This may be down to the fact that the temperature was not constant and may have affected the rate of reaction. Keeping the temperature constant was difficult because sometimes the temperature would decrease or increase than the wanted temperature. This meant that at times the recordings were slightly inaccurate. I overcame this problem by moving the Bunsen burner away from underneath the tripod when the temperature was too high. And I did the opposite when the temperature was too low, I placed the Bunsen burner under the tripod again to increase the temperature back to the wanted temperature. In future, I would like to find out how concentration affects the rate of reaction of the same experiment that I have done.

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