We can also time how quickly reactants are used up. The quicker these things happen, the faster the rate of the reaction. If a reaction has a low rate that means the molecules combine at a slower speed than a reaction with a high rate. Some reactions take hundreds, maybe even thousands of years while other can happen in less than one second. The rate of reaction depends on the type of molecules which are combining.
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The collision theory says that the more collisions in a system, the more likely combinations of molecules will happen. So if there are a higher number of collisions in a system, more combinations of molecules will occur, the reaction will go faster, and the rate of that reaction will be higher. Activation energy is the energy needed for a collision to happen. Even if the species are orientated properly, you still would not get a reaction unless the particles collide with a certain minimum energy called the activation energy of the reaction. Activation energy is the minimum energy required before a reaction can occur.
What can affect the rate of reaction?
Surface area can affect the rate of reaction. The more finely divided the solid is, the faster the reaction happens. A powdered solid will normally produce a faster reaction than if the same mass is present as a single lump. The powdered solid has a greater surface area than the
single lump. You are only going to get a reaction if the particles in the gas or liquid collide with the particles in the solid. Increasing the surface area of the solid will increase the chances of collision taking place.
The concentration of the reaction also affects the rate. For many reactions involving liquids or gases, increasing the concentration of the reactants increases the rate of reaction. In a few cases, increasing the concentration of one of the reactants may have little noticeable effect of the rate. In order for any reaction to happen, those particles must first collide. This is true whether both particles are in solution, or whether one is in solution and the other a solid. If the concentration is higher, the chances of collision are greater.
Pressure may also be a factor in a reaction. Increasing the pressure on a reaction involving reacting gases increases the rate of reaction. Changing the pressure on a reaction which involves only solids or liquids has no effect on the rate. Increasing the pressure of a gas is
exactly the same as increasing its concentration. If you have a given mass of gas, the way you increase its pressure is to squeeze it into a smaller volume. If you have the same mass in a smaller volume, then its concentration is higher. In order for any reaction to happen,
those particles must first collide. This is true whether both particles are in the gas state, or whether one is a gas and the other a solid. If the pressure is higher, the chances of collision are greater.
As you increase the temperature the rate of reaction increases. As a rough approximation, for many reactions happening at around room temperature, the rate of reaction doubles for every 10°C rise in temperature. You have to be careful not to take this too literally. It doesn’t apply to all reactions. Even where it is approximately true, it may be that the rate doubles every 9°C or 11°C or whatever. The number of degrees needed to double the rate will also change gradually as the temperature increases.
Hypothesis: I assume that with the increase in temperature, the reaction between sodium thiosulphate and hydrochloric acid will be fast. This should happen because the heat energy and the kinetic energy would make the particles move faster, collide faster and ultimately react faster. Hence the bonds will be broken easily.
A small increase in temperature causes significant changes to the distribution energies. At the higher temperature:
1. The peak is at a higher energy.
2. The peak is lower.
3. The peak is broader.
4. There is a large increase in the number of particles with higher energies.
5°C to 70°C
0s to 60s
Possible effect on results
Method to control
Concentration of the reactants
Increasing or decreasing the concentration would alter the rate of reaction. As increasing the concentration results in increase in the rate of reaction.
The reactants used will be of the same molarity throughout the experiment, 1M
Volume of the reactants
Even after controlling the concentration, difference in the volume of the reactants would lead to inaccurate results. If you have the same mass in a smaller volume, then its concentration is higher which would give us wrong results.
Equal amount of reactants are used in performing this investigation.
All the apparatus used in performing this experiment should be of the same scale and measurement, so that there is no difference in the final results.
15 conical flasks
15 measuring cylinder
15 10″x 10″ square papers with an X
Take a measuring cylinder and pour 20cm3 of sodium thiosulphate into 3 test tube to yield more results in 5 different situations, that is
Beaker with ice only.
Beaker with boiling water.
½ boiling water and ½ tap water.
Only tap water.
A small amount of ice in tap water.
With the help of another measuring cylinder pour out 20cm3 of hydrochloric acid in 3 conical flasks for the first situation.
Use a beaker to setup a temperature for different situations listed above, by putting the 3 test tubes with sodium thiosulphate inside the beaker.
Once the thiosulphate is at a suitable temperature, place the square paper with an X under the three conical flasks with HCl. Prepare the stopwatch. As soon as you pour the thiosulphate into the HCl start the stopwatch. Stop the stopwatch when you are no longer able to see the X under the conical flask.
Repeat the steps 1-4 for every different situation. The raw data yielded out of this experiment should be recorded as shown in the table below.
Ice in tap water
Half boiling water and half tap water
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