3.2 - Rates of reaction Flashcards
Explain the disappearing cross method?
-Measure sodium thiosulfate into a flask
-Measure dilute hydrochloric acid into a measuring cylinder
-Draw a cross on a piece of paper and put it underneath the flask
-Add the acid into the flask and start to stopwatch look down at the cross from above and stop the stop watch when the cross can no longer be seen
-repeat with lower concentrations of sodium thiosulfate solutions calculate mean values for each concentration never include anyolmeus solutions
Explain the results of the disappearing cross method?
With an increase i the concentration of a solution the rate of reaction will increase this is because there will be more reactant particles in a given volume, allowing for more frequent and successful collisions. Increasing the rate of reaction.
What is the problem using the disappearing cross method
different people have different perceptions of when the cross has disappeared. Some may see the cross for longer so results may be different. Using different sized cross as well.
Explain the method for the effect of catalyst on the rate of reaction?
-Add dilute hydrogen peroxide into a conical flask
-Use a delivery tube to connect this flask to a measuring cylinder upside down in water
-Add the catalyst magnesium oxide into the conical flask and close the bung
-Measure the volume of gas produced in a fixed time using the measuring cylinder
-Repeat experiment without the catalyst and compare results every 10 seconds measure the volume of hydrogen gas given of in the cylinder until no more is given off
What are the factors that can affect the rate of reaction?
-Concentration of the reactants in solution
-Tempreture at which the reaction is carried out
-Surface area of the solid reactants
-The use of catalyst
Explain the method of effect of surface area on the rate of reaction experiment
-Add dilute hydrochloric acid to the conical flask
-Use a delivery tube to connect this flask to an inverted measuring cylinder upside-down in water
-Add calcium carbonate chips into the conical flask and close the bung
-Measure the volume of gas produced in a fixed time in the measuring cylinder this can be used to determine the rate of reaction
-Measuring the volume of gas can be difficult using a measuring cylinder more accurate results by using a gas syringe as the bubbles will be slower
Explain the effect of tempreture on rates of reaction experiment
-Dilute hydrochloric acid is heated to set tempreture using a water bath
-Add the dilute hydrochloric acid into a conical flask
-Add a strip of magnesium and start the stop watch and repeat at different tempretures and compare results.
What are the results of increasing the tempreture on rates of reaction
With an increase in the tempreture the rate of reaction will increase this is because the particles will have more kinetic energy than the activation energy that is required therefore more frequent and successful collisions will occour increasing the rate of reaction
What does increasing the concentration of a solution do to the rate of reaction
At a higher concentration there are more reactant particles in the some volume. Because there are more particles in the same volume there is an increased change of more successful frequent collisions this means that the rate of reaction will be increased
If the number of particles is doubled in the same volume the number of collisions per second will also be doubled the number of collisions is proportional to the number of particles present. In gases the rate of reaction can be increased by increasing the gas pressure to bring the particles closer together this increased the frequency of collisions.
What does increasing the tempreture do to the rate of reaction
Chemical reactions can only take place when the reacting particles collide with each other. The collisions must have sufficient energy more energy than the activation energy. The rate of a chemical reaction is determined by the frequency of successful collisions per second.
-The activation energy is the minimum amount of energy that the particles must have in order to react and collide successfully.
-If two particles colide with a low amount of energy they cannot overcome the activation energy barrier no reaction would occour as they do not collide successfully. If two particles with a large amount of energy collide they will have enough energy to overcome the activation barrier and collide successfully a reaction would take place because of this
-Increasing the tempreture increases the rate of chemical reactions. This is because the particles will have more kinetic energy so they will move faster and have more frequent collisions, more energy than the required activation energy therefore there will be more frequent and successful collisions per second increasing the rate of reaction. Because the rate of reaction increases with tempreture the rate of reaction is proportional to the tempreture.
What does increasing the surface area of a solid do to the rate of reaction
Increase in the surface area of the marble chip, the rate of reaction will increase
This is because more surface area particles of the marble chips will be exposed to the dilute hydrochloric acid so there will be more frequent and successful collisions, increasing the rate of reaction
explain collision theory
-In order for particles to react they must collide they cannot react if they do not collide, when particles react chemical bonds must be broken, which requires energy. For this to occour particles must colide with enough energy to start breaking the chemical bonds. If the collision does not have enough energy then the particles cannot react and will just simply bounce of each other. Particles must colide in the correct orientation and with sufficient energy. The rate of reaction is proportional to the number of successful collisions per second . The frequency of successful collisions. On way to increase the rate of reaction is to increase the concentration of a solution.
What are catalyst?
-Catalyst are substances which speed up the rate of a chemical reaction without themselves being altered or used up during the reaction, because catalyst are not used up during the reaction they can be used repeatedly
What do catalyst do to the rate of reaction
- The rate of a chemical reaction depends on the number of particles that have enough energy to cross the activation energy barrier and collide successfully. Catalyst increase the rate of reaction by providing an alternative pathway for the reaction that has a lower activation energy for the reaction t occour. When a catalyst s present the particles require less energy to cross the activation energy barrier. This means that more particles can successfully collide per second this increases the rate of reaction.
-Catalyst are not included in the chemical equation for a reaction this is because they are not used up in the reaction, Catalyst are not a reactant. Different reactions need different catalyst.
-They provide an alternate pathway for the reaction to occour by lowering the activation energy requiring less energy
What are exothermic reactions?
-Exothermic reactions transfer energy from the reacting molecules to the surrondings so during an exothermic reaction the tempreture of the surrondings increases. Combustion is an exothermic reaction which is burning. Other exothermic reactions include certain exothermic reactions and neutralisation. The energy changes that take place in reactions can be represented by drawing an energy profile diagram.
