In this experiment I shall be investigating how temperature affects the rate of reaction
Rates of reaction
The Factors that affect the rate of reaction are temperature, surface area, concentration, catalysts, light and pressure
Surface area – Surface area is the amount of solid surface that is available for reaction – Only affects solids so this will not affect our experiment
– When the surface area increases the rate of reaction increases as there is more surface area for the particles to work on, thus, there are more collisions per second
– Example : It is easier to light a fire with small pieces of stick than using large blocks of wood
Concentration – Concentration is the amount of molecules of a substance in a given volume
– Concentration affects solids, gases and liquid so this will affect our experiment – When the concentration increases the rate of reaction increases as there are more molecules present, therefore there are more collisions between molecules (Collision theory) – Example : zinc reacts fairly slowly with dilute hydrochloric acid but when the acid is concentrated, the rate of reaction increases.
Catalysts – A catalyst is a substance which speeds up the rate of reaction without itself going undergoing any permanent chemical change – this means only small amounts of catalysts are needed to speed up reactions
– When a catalyst is involved in an experiment there is less energy needed for the reaction therefore there is more collisions per second – We will not be using catalysts in our experiment – Example : Decomposing hydrogen peroxide solution at room temperature is very slow, but using a small amount of manganese oxide greatly increases the reaction rate and oxygen is given off rapidly
– Light is a form of energy and it causes many chemical reactions to take place.
– Light does not affect our experiment
– Example : Photosynthesis
Collision theory is used to explain how different factors affect the rate of a chemical reaction. For a reaction to take place the reactant particles must collide with each other with adequate energy (activation energy), this energy is used to break the bonds between the particles. If the particles do not have enough energy they will bounce off each other without reacting. By increasing the temperature the particles gain more energy and move faster causing more collisions per second.
These previous experiments give us background information on rates of reaction:
Acid and limestone
CaCO3(s) + 2HCL(aq) CaCl2(aq) + H2O(l) + CO2(g)
Apparatus – Conical flask, hydrochloric acid, marble chips, cotton wool and scales
In this experiment we mix a certain mass of large marble chips with a certain volume of hydrochloric acid in a conical flask and use cotton wool to trap the acid spray. As the carbon dioxide is given off from the flask, the mixture loses mass, this is measured and recorded every minute until the reaction is over. The experiment is repeated again using the same mass of marble chips and the same volume of hydrochloric acid and the same temperature but instead using small marble chips. When we look at our results we find that the larger marble chips take more time to react than the smaller marble chips which show that as the surface area increases, the rate of reaction increases.
Decomposition of hydrogen peroxide solution
H2O2(aq) 2H2O(l) + O2(g)
Apparatus – Conical flask, gas syringe, hydrogen peroxide solution and solid manganese oxide
In this experiment we firstly measure the time taken for hydrogen peroxide to decompose and produce 50cm3 of oxygen at room temperature and without a catalyst. We use a gas syringe to measure the oxygen given off. Then we repeat the experiment but instead add a small amount of solid manganese oxide to the hydrogen peroxide solution. When we look at our results we find that without the catalyst (manganese oxide) the reaction is very slow, but when we add the catalyst the decomposition is very fast and oxygen is rapidly given off which shows that catalysts increase the rate of reaction.
Sodium thiosulphate and hydrochloric acid
Na2S2O3(aq) + 2HCL(aq) 2NaCl(aq) + SO2(g) + S(s) + H2O(l)
Apparatus – Sodium thiosulphate, hydrochloric acid, stop clock, a measuring cylinder and white paper with a black cross
In this experiment we vary the concentration of the sodium thiosulphate, add it to a given volume of hydrochloric acid and time how long it takes for the mixture to go cloudy and the cross to disappear. When we look at our results we see that as we increase the concentration of sodium thiosulphate the rate of reaction increases.
My prediction is, as the temperature of the reaction mixture increases so to will the rate of reaction as at higher temperatures the particles have more energy and will collide more hence increasing the rate of reaction. This is explained by the collision theory. The collision theory also allows me to predict that my time against temperature graph will have negative correlation as the time taken will decrease as the temperature increases. I also predict this graph will be curved as the time taken will not be directly proportional to the temperature. I also predict that as I increase the temperature of the mixture, the time taken for the cross to disappear will decrease.
In my experiment I shall be investigating the effect of temperature on a reaction rate by reacting sodium thiosulphate in dilute hydrochloric acid as shown in the equation below
Sodium + hydrochloric Sodium + Sulphur + Sulphur + Water thiosulphate acid chloride dioxide
Na2S2O3 (aq) + 2HCL (aq) 2NaCl (aq)+ SO2 (g) + S (s) + H2O (l) Sodium thiosulphate is a clear liquid and hydrochloric acid is a clear liquid, when they react together the solution turns cloudy due to the sulphur.
The reaction is exothermic as the energy required to break the bonds is less than the energy needed to make new bonds.
• Conical flask
• Measuring cylinder
• Bunsen burner
• Stop clock
• White paper with a black cross
1. Measure out 10 cm3 of sodium thiosulphate and 40cm3 of water into a flask. Measure out 5 cm3 of hydrochloric acid an a measuring cylinder 2. Heat the thiosulphate solution to the required temperature using a Bunsen burner 3. Add the acid and start the stop clock. Swirl the flask to mix the solutions and put the solution on the white paper with a black cross 4. Look down at the cross and stop the clock and note the time taken when the cross has disappeared. Record the temperature of the mixture in the flask.
The variables we will need to keep constant are
• The concentration of sodium thiosulphate
• The concentration of hydrochloric acid
• The volume of hydrochloric acid
• The same colour of cross
• The same thickness of cross
• Look at the cross from the same height
The independent variable is the temperature. We will take 7 different recordings between 10o-70o We will do each recording 5 times and get an average to make sure the results are accurate.
I will record my results in the table and make a time against temperature and a 1/time against temperature graph as shown below