They do not need a lot of energy to be able to collide. Catalyst make much easier for particles to react. Catalysts increase the rate of a reaction by helping break chemical bonds in reactant molecules. This effectively means the Activation Energy is reduced. Therefore, at the same temperature, more reactant molecules have enough kinetic energy to react compared to the uncatalysed situation. Although a true catalyst does take part in the reaction, it does not get used up and can be reused with more reactants. A solid catalyst might change physically by becoming more finely divided, especially if the reaction is exothermic.
Effect of surface area
The more surface area, more collisions happened and faster the rate of reaction
Effect of Particle Size
The smaller the size of the particle the faster the reaction.
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There are two graphs two the effect of the temperature on the rate of the reaction:
- The higher the temperature the higher the rate of reaction.
- If the temperature is high, it takes a long time for reaction
This pictures I found in the Internet on the page:
www.google.com/graphschem.html.com
To investigate the effect of the temperature on the rate of the reaction, we will use such reaction:
a) Marble chips and hydrochloric acid- to find out the mass loss;
b) Magnesium and acid- to find out how much hydrogen is produce in minutes;
c) Sodium and hot water-to find out how long it take to the reaction occurs;
d) Potassium and water- to find out how long it take to react with water;
e) Iron in copper sulphate solution - to find out how long it takes to the reaction occurs
f) Sodium thiosulphate and acid- to find out the effect of the temperature on the rate of the reaction.
Na2S2O3 + 2HCI 2NaCl + H2O + S + SO2
For the experiment I choose sodium thiosulphate+hydrochloric acid reaction, to measure the effect of the temperature on the rate of the reaction. The theory behind this experiment is that ‘Increasing the concentration can increase the rate of the reaction by increasing the rate of molecular collisions.’ It is easy to do, accurate to measure the temperature and it is very quickly. In addition, the sulphur is a solid, so you can measure how quickly the water becomes cloudy, how long it takes for the reaction to occur. You can see every time new changes, as higher the temperature as faster it goes cloudy.
Our safety:
- Wear goggles at all times
- Take care with acid
- Heat all apparatus in the centre of the bench rather than the edge
- Do not inhale the sulphur being produced
- All the usual safe lab practices
- You should use gloves if a tube is hot or tongs
- Do not put your head very close to liquids when you want to look at the cross
- Do not sit while the experiment
- Do not leave experiment unattended
- After the experiment do not forget to wash your hands
- Do not forget tie up your hair
I did a pre-test and for my experiment I used:
- 20 ml of sodium thiosulphate;
- 40 ml of distilled water;
- 5 ml of hydrochloric acid;
How to do this experiment
- Make up about 200ml of a dilute sodium thiosulphate solution by adding 8g of sodium thiosulphate to 200ml of water (concentration – 4%)
- Mark an X (big cross) on a piece of white paper and place the conical flask over it.
- Put 60ml of the thiosulphate solution into the conical flask.
- Now get a watch ready (a stopwatch is better but an ordinary watch with second indicators okay):
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Add 5ml of hydrochloric acid and start swirling the conical flask. Count the number of seconds until the X disappears (due to the cloudiness of the sulphur which starts appearing).
To watch the X look down from the top through the solution.
- Take the temperature at the end.
The person timing the experiment will look for the disappearance of the cross, otherwise there would be a time lapse between seeing the cross disappear and telling the other person to stop the clock and then eventually stopping the clock, we will time it to the nearest seconds. To keep constant we do not change the cross, we do the same experiment and do not mix tubes because we can damage the solution, which we will need to continue our experiment. Also if I want to make sure that the temperature which I chose is the actual temperature I will need to use the thermometer to measure the temperature. I think if use the thermometer right way I will get the accurate results as it possible. I think we wont need to do duplicates, because we cant do the same temperature and it wont be as accurate as it can be.
I think my results are good enough, because we were doing it really careful. We were doing the10 readings because it’s a minimum to get the possible, right results. We used thermometer to check the temperature, also we used stopwatch to check if the reaction is fast or slow.
To describe my experiment, at first I will set up my apparatus. Then I will wear safety goggles and lab coat. Then I will need two beakers and label one of then as acid and another as sodium thiosulphate. Also I will need a cross on a piece of paper and set up the Bunsen burner on a mat underneath a tripod and gauze. To measure acid, I will need ac measuring cylinder, conical flask, stopwatch, thermometer and pipette.
This is a diagram of my apparatus, which I will use for my experiment
After I set up my apparatus out, I will measure the amount of the sodium thiosulphate and hydrochloric acid. I will pour sodium thiosulphate into the beaker, which was labelled as sodium. And I will use another cylinder to measure the acid. Turn on the gas and light the bunson burner, but do not do it underneath the tripod for it is in an awkward place and you might burn your self. I will use the conical flask because I need to mix the water and the sodium thiosulphate together, then I will heat it up to the temperature that has been written. To know if it is right or not I will use the thermometer to get the correct temperature. Once it has been done I will take it off and pour 5 ml of acid and put it on the cross, swirl. Someone will get a stopwatch to stop the stopwatch and time the time. The mixture will start to go cloudy and we cannot see the cross. And then I will record my results from the stopwatch, temperature from the thermometer after I will do the same experiment but I will change the temperature each experiment 10 times.
I will need to have at least 10 results to get an accurate experiment. Each experiment I change the temperature and I can compare and see difference between them. In the end I can make a good graph of the results.
Conclusion
Our results shows how long it takes to the reaction to occur and the effect of the temperature on this reaction. If the temperature increases then the rate increases because the time decreases. From my graph, I can see that if the temperature is 60°C it will take 13 second, but for 25 C I will need 87 seconds to see the reaction. Our graph is curve as you can see above, because the rate increases more rapidly than temperature. The temperature gives more energy to the particles and that’s why they move faster and collide harder and there are more collisions happened.
I think our results look similar to others groups, but we cant have the same because we used different reactants for our experiment t. I took a table results from the other group to compare our results.
As well, we have the same the shape and that is why we can say that our results are very similar to their results.
Our experimental results were very similar to our predictable results. We can see from the graph that the main pattern of the line was the same. The one main difference was that we have done only 10 readings but prediction produced using five readings only. The gradient of the graph is steeper after 60ºC.
Evaluation
Our experiment was done very good. We have done very carefully this experiment because we wanted to have more exact results. I enjoy doing these experiments because you start to learn new things and to see how can affect the temperature on the rate of the reaction and you can see what can happened if you mix water, sodium thiosulphate and acid. We were using all apparatus to the right degree of accuracy, for example,” We use thermometer to the nearest degree, then if we need a measuring cylinder to measure the 5 ml, we can find a cylinder which only for 5 ml and we don’t have to measure many times to get the right number of acid or some reactants, also in our experiment we used the stopwatch and we rounded it to the nearest second”. Therefore we did not have any anomalous results that did not fit the pattern. The experiment was suitable way of carrying out the experiment. We can not assume that results were very accurate and reliable but other less it look like line of best fit and it better way to find out the rate of the reaction. I found the most of information in the book, which called “Key science book-Chemistry” and my graphs looked very similar to the book graphs and some of the results looked similar that’s why I found that my results are not very bad. There are most reliable and good enough for this experiment.
I assume we did enough experiments and the range was wide enough, for example, we took from 25º C to 70º C and we do ten experiments and it was enough to see the changes between them.
We could have some problem while carrying out the experiment with pipette, tubes and sodium thiosulphate. For example pipette we can take a one pipette and use it for acid, but then we can just forget that we used it already in acid, we can use it for sodium and after we need to pour out the two solution and waste them and that’s why you keep doing new, and you waste your time, that we should more carefully.
I estimate that it was much easier and it can give the good results and its very interesting. Now I will set up another experiment that could be carried out to extend out this work and provide you with more evidence. I will take the experiment between marble chips and hydrochloric acid. To find if changing the concentration of an acid will increase or decrease the rate of the reaction when marble is dissolved in hydrochloric acid. With the equation Ca CO3 + 2 HCl CaCl2 +H2O + CO2. A reaction occurs when particles collide. This process is based on random particle movement, so therefore, the more particles you have in a space, the more likely they are to collide. Therefore making the reaction accelerate. When the concentration of acid increases, more gas will be given off faster. I know this from my trial experiments. Since I will be working with strong acid, I will wear safety goggles while conducting the experiment.
I will use Marble chips all of a small size. I can use a sieve to make sure they are all roughly similar size- about 7mm diameter.
The amount of acid I have decided on is 10ml. And so the amount of marble must be in excess - 3g.
I can measure the speed of the reaction by how much gas is given off. I can measure this in cm3 in a gas syringe. When the experiment takes place, I will take the reading every 10-second to get a good graph for the results. If the reaction goes very quickly, I will take the readings every five seconds. I learnt from the trial experiments that it is quite hard to start a stopwatch, pour acid and stick a bung into a boiling tube all at the same time, so I will get someone to assist me while doing so.
If the experiment goes on for a ridiculous time, I will cut it off. I don't think it is necessary to have the experiment go over three minutes, so I will cut it off then. Also, if the amount of gas goes off the scale I will stop it there.
It is important to keep the starting temperatures constant for all the reactions as this can affect the results by giving the particles more energy (and making it faster). Think that the best way of displaying these results is by drawing a line graph. In it, I have used the average of the two sets of results. The pattern I can see is that when the reaction first starts, the reaction is fastest, from then on, the reaction slows. We can see this because the gradient of the curve is steepest at the beginning.
The cause of this curve is that at the start of the reaction, there are the most amounts of acid molecules that are colliding with the marble.
