For a chemical reaction to take place, some bonds in the reactants must be broken. The colliding particles must have enough energy to break these bonds. This minimum amount of energy is called the activation energy. Only the very fastest moving particles have enough energy to break bonds.
In gases, liquids and in solution, the particles move at a range of speeds. Some are moving very slowly and others are moving very fast. To react, particles must collide with enough energy and in the correct orientation for bonds to be broken. Below you can see what happens between particles when they don’t have sufficient amounts of energy to start off a reaction.
The particles are moving The particles The particles rebound and
around. collide to move again.
This didn’t cause a reaction because the particles didn’t have enough energy to brake the bonds. Below you can see what would happen if they did have enough energy.
The particles are moving The particles collide A reaction has taken
around and break the bond place and the new substance
is formed.
You can see that the particles did have enough energy to brake the bonds so therefore a new substance was formed. This needs to happen is any reaction is going to take place. The particles gain more energy from heat. So the higher the temperature, the faster the particles will be moving and the more energy the particles will have.
The two theories that affect temperature and the rate of reaction are the “kinetic theory” and the “collision theory.” These theories helped me understand how changing the temperature was going to affect the rate of the reaction because the kinetic theory states that the positioning and movement of particles in a substance increases as the temperature increases. This means that if the particles are moving faster there are going to be more frequent collisions and therefore the rate of reaction is going to increase. This will only happen if the particles collide with enough energy to break the existing bonds and bring reactive sites closer together.
Prediction
From the research I have performed I have been able to make a suitable prediction.
The rate of a chemical reaction is the speed at which the reaction takes place. Temperature is a major factor in this. Increasing or decreasing the temperature changes the movement of particles in a substance therefore changing the rate of reaction. When a reaction mixture is heated up, each particle in it gets more energy and collides more with other particles.
Thus, from the research I have collected, I can make the prediction that if you increase the temperature of a particular reaction, you increase the speed at which it takes place. This is simply because the particles carry more energy and collide more often where these collisions contain enough energy to break the energy barrier.
Below is a graph of the reaction times:
This graph shows us the relation of temperature and rate of reaction. This clearly shows that as the temperature increases then the rate of the reaction also increases. Therefore I can predict that the cross wil disappear quicker, the higher the temperature is.
Apparatus
For this experiment I am going to need:
- Sodium thiosulphate solution (40g/litre)
- Hydrochloric acid (2M)
- Water
- 250 cm³ chronicle flask
- -5ºc – 110ºc thermometer
- 10cm³/50cm³ measuring cylinder
- Heat proof mat
- Bunsen burner
- Wire gauze
- Tripod
- Stopwatch
- White tile
- Sheet of plain A4 paper
- Pen
Trial Experiment
For my trial experiment, I did the experiment but did not repeat it five times as I only wanted to make sure that the apparatus I was using was accurate and to familiarise myself with the experiment. This trial experiment helped me to plan my actual investigation better as I learnt from my mistakes. These were things like not starting the stopwatch, quick enough, which changed the times of my results, and using a little too much hydrochloric acid (10cm³ when I should have used 5cm³) that again made my results inaccurate.
Therefore, in the actual experiment I am going to use syringes to measure the chemicals to get them accurate and start the stopwatch at the exact time the hydrochloric acid is added to again ensure fair and precise results.
Below is a table of my results:
Safety
To make sure that my experiment is going to be safe for me and the people around me I am going to wear safety goggles at all times to protect my eyes from dangerous substances. I am also going to wear a lab coat so not to get any chemicals on either my clothing or myself. I am also going to use books to find out the dangers of each of the chemicals I am going to be using and what safety measures needed to be taken. I will also use a heatproof mat to protect any work surfaces. When using the Bunsen burners I am going to be extremely careful throughout the experiment. I know that sulphur is a dangerous chemical and I must be very cautious when near it because it can irritate your skin and this also applies for the acids, which can be very corrosive. Any spills of acid should be wiped up immediately with water. I must also be sure not to inhale any of the sulphur dioxide that is given off during the experiment as it is poisonous.
Fair Test
To make my experiment a fair one, I will have to look at a lot of things. Firstly, I will need to look at the factors that may have affected how well the investigation would work and these were things like using different equipment or doing the actual experiment in different conditions i.e. a colder/hotter environment. To combat this, I need to make sure that upon repeating the experiment, I used the exact same equipment and do it in the exact same environment to make absolutely sure that the experiment is fair at each temperature.
I think that these are both very important factors because they could affect the results severely and leave me with unreliable results when I should only have reliable results. To ensure fair and accurate results, all of the factors that can affect my results need to be controlled. I must use the same piece of paper with the same cross on it. I must also use the same measuring cylinders to measure my chemicals. The same stopwatch must also be used and the same person should control each of the controlled factors every time. So the person using the stopwatch remains the same and the person measuring the chemicals stays the same. This way the results will be more reliable because each individual’s reaction time so if we changed people then there would be an inaccuracy with the timing. Exactly 20cm³ of sodium thiosulphate must be used each time as well as exactly 5cm³ of hydrochloric acid. These measurements need to be exact to make the experiment fair.
Reliable Results
To make my results as reliable as possible I am going to repeat each temperature 5 times, ranging from room temperature and 60ºc. That is seven different results altogether, from which I can make a good average to plot onto a graph so that I can easily observe and patterns or faults.
I will also make sure that each temperature is calculated to as accurate as it can be as recording a result past the required temperature can mean unreliable results which makes the entire investigation unreliable as one result is not calculated correctly.
Method
- Draw a cross on your A4 paper.
- Measure 20cm³ of sodium thiosulphate using the chronicle flask.
- Measure out 5cm³ of hydrochloric acid using a 10cm³ measuring cylinder.
- Heat water bath to the appropriate temperature.
- When the temperature is correct pour 5cm³ of hydrochloric acid into the flask containing the sodium thiosulphate and start the stopwatch.
- Place over the black cross and shake gently until you can no longer see the black cross.
- As soon as you cant see the cross stop the stopwatch.
- Record the time.
- Repeat 5 times.
- Do steps 1-10 for each temperature.
