topic 7 - rates of reaction and energy changes

state the METHOD to investigate the effects of changing the conditions of a reaction on the rates of chemical reactions (GAS)

1. support a gas syringe with a stand, boss and clamp

2. using a measuring cylinder, add 50cm³ of dilute hydrochloric acid to a conical flask

3. add 0.4g of calcium carbonate to the flask

4. immediately connect the gas syringe and start the stop clock

5. record the time for every 10cm³ of gas produced for 5 minutes

6. when the reaction is complete, clean the apparatus

7. repeat the experiment for different concentrations, recording time and concentration in a table

state the ANALYSIS of the investigation the effects of changing the conditions of a reaction on the rates of chemical reactions (GAS)

• for each concentration of hydrochloric acid, plot a graph on the same set of axes to show:

  • volume of gas (cm³) on the y-axis

  • time on the x-axis

  • a curve of best fit

  • for each concentration of acid, plot a graph to show:

  • mean rate of reaction = total volume of gas produced / reaction time
    

state the METHOD to investigate the effects of changing the conditions of a reaction on the rates of chemical reactions (COLOUR CHANGE)

1. using a measuring cylinder, add 50 cm³ of dilute sodium thiosulfate solution to a conical flask

2. place the conical flask on a spotting tile with a black cross drawn on it

3. using a different measuring cylinder, add 10cm³ of dilute hydrochloric acid to the conical flask

4. immediately swirl the flask to mix its contents and start a stop clock

5. measure and record the temperature of the reaction mixture

6. look down through the reaction mixture. When the cross is no longer visible, record the time on the stop clock

7. measure and record the temperature of the reaction mixture and clean the apparatus

8. repeat the experiment with different starting temperatures of sodium thiosulfate solution

state the ANALYSIS to investigate the effects of changing the conditions of a reaction on the rates of chemical reactions (COLOUR CHANGE)

• calculate 1000/time for each temperature (this value is proportional to the rate of reaction)

• plot a graph to show

  • reaction rate on the y-axis

  • temperature on the x-axis

  • a curve of best fit

explain collision theory

• when reactants come together with kinetic energy, their particles will collide

  • some of these collisions will result in chemical bonds being broken and some new bonds being formed

• increasing the frequency of successful collisions means that a greater proportion of reactant particles collide to form product molecules

• not all collisions result in a chemical reaction

  • unsuccessful collisions happen when the colliding species do not have enough energy to break the necessary bonds

  • if they do not have sufficient energy, the collision will not result in a chemical reaction

explain how the concentration of a solution affects the rate of reaction

• increasing concentration of solution will increase the rate of reaction

• as there will be more reactant particles in a given volume, allowing more frequent and successful collisions per second

• the number of collisions is proportional to the number of particles present

explain how the concentration of a solution affects the rate of reaction

• increasing temperature increasing the rate of reaction

• because the increase in temperature increases the kinetic energy of the particles

• meaning there will be more frequent and successful collision per second

• effect of temperature on collisions is not linear; small increase in temperature causes a large increase in rate

explain how the surface area of a solid affects the rate of reaction

• increasing surface area of a solid reactant increases rate of reaction

• because larger surface area of the particles means more of it will be exposed to the other reactant

• producing a higher number of collisions per second

• surface area of solid and rate of reaction is proportional

catalyst definition

• substance that speeds up the rate of a reaction

• without altering the products of the reaction

• and itself being unchanged chemically and in mass

• at the end of the reaction

explain how the addition of a catalyst increases the rate of reaction

• catalysts provide an alternate route for the reaction to occur

• this happens by lowering the activation energy required

• thus providing a reaction pathway requiring less energy

state why catalysis is important in chemistry

• increases rate of reaction/production rate

• reduces energy costs

recall what enzymes are

biological catalysts

state what industry enzymes are used in

production of alcohol drinks

state when changes in heat energy occur

• salts dissolving in water

• neutralisation reactions

• displacement reactions

• precipitation reactions

state what needs to be measured when changes in heat energy occur in a solution

• temperature changes

• using a thermometer

• to reflect the heat changes

exothermic reaction/change definition

• change/reaction

• in which heat energy

• is given out

endothermic reaction/change definition

• change/reaction

• in which heat energy

• is taken in

state what type of reaction breaking of bonds is

endothermic

state what type of reaction making of bonds is

exothermic

state when a heat change is exothermic

• if more heat energy is released

• in forming bonds in the products

• than is required in breaking bonds

• in the reactants

state when a heat change is endothermic

• if less heat energy is released

• in forming bonds in the products

• than is required in breaking the bonds

• in the reactants

explain how calculate the energy change in a reaction (given the energies of bonds)

• energy change = energy taken in - energy given out

• measured in kJ/mol

explain the term activation energy

• minimum energy needed

• for successful collisions

• where atoms within the reactants

• rearrange to form products

explain how to draw a reaction profile for endothermic reactions

• energy is taken in endothermic reactions

• energy of the products will be higher than the energy of the reactants

• so the change in energy is positive

• this is represented on the reaction profile with an upwards arrow

• horizontal line to the left of the positive curve is the reactants

• horizontal line to the right of the positive curve is the products

• activation energy is the maximum value of the curve

explain how to draw a reaction profile for exothermic reactions

• energy is given out in exothermic reactions

• the energy of the products will be lower than the energy of the reactants

• so the change in energy is negative

• this is represented on the reaction profile with a downwards arrow

• horizontal line to the left of the negative curve is the reactants

• horizontal line to the right of the negative curve is the products

• activation energy is the maximum value of the curve