Other factors change reaction rates. If reacting substances are heated, the rate of the reaction usually rises; conversely, if they are cooled, the reaction slows down. In order to react, the particles in the substances must collide with each other. Heat gives them more energy to move around and so increases the chances of a collision. Also, when particles do collide, they are more likely to react, rather than just bounce off each other, if they are moving faster. Cooling has the opposite effects. For example, when sodium thiosulphate is mixed with dilute hydrochloric acid the mixture becomes cloudy as solid sulphur comes out of the solution (precipitates). If the mixture is heated, it becomes cloudier more quickly. If it is cooled, it takes longer to become cloudy.
The rate of a reaction can be obtained by following some measurable property that alters as the reaction occurs. Examples of such measurable properties include gas volumes, concentration of reaction mixture, and electrical conductivity.
2HCl + Na2S2O3 2NaCl + S + SO2 + H20
Prediction: I predict that as the temperature is increased the rate of reaction will increase. I also predict that as the concentration of the sodium thiosulphate increases the rate of reaction will increase.
Key Factors:
- Temperature
- Concentration
- Time
Independent Variable: The temperature
Dependant Variable: The time
Control Variables:
- The concentration
- The amount of sodium-thiosulphate solution put into the flask
- The amount of dilute hydrochloric acid put into the flask
Collision Theory: Before we can get a chemical reaction, particles must crash together. They must collide. The more collisions between particles in a given time, the faster the reaction. In all collisions momentum is conserved (the total momentum of two colliding objects before and after their collision remains the same). This is a universal physical law, and is a consequence of the truth of Newton’s second and third laws of motion.
Safety: I will make sure I am safe by checking with my teacher that the acids and apparatus are safe to use and by checking the symbols on the acids to see whether they are dangerous or not. I will also wear safety goggles and an apron to protect myself, and when handling hot beakers and measuring cylinders a pair of tongs will be used.
Apparatus:
- 2 thermometers
- 1 beakers
- 2 measuring cylinders
- 1 conical flask
- 1 tripod
- 1 gauze
- 1 clock
- 1 Bunsen burner
- 1 pair of tongs
Results:
Graph Of Results:
Evaluation:
I don't think my results were reliable enough to draw an accurate conclusion to how temperature affects the rate of reaction, however they did prove my basic theory. To improve my results I could have done more preliminary work to make sure my method was as accurate as possible and that I was more familiar with doing the experiment.
If I was to extend the experiment I could try seeing how different variables affect the rate of reaction, for example the concentration of acid. Before doing this, I think it would be a good idea to repeat the experiment investigating temperature to improve my results.
Conclusion:
From my results I can see that my prediction was correct and the time it took for the cross to disappear did decrease as the temperature was increased. I could carry on past 80º to see if the trend continued but it would eventually become too difficult to get an exact time.
