Topic 7.1-7.8 - Rates of reaction Flashcards
How do you carry out the core practical to investigate changing the conditions in the reaction between hydrochloric acid and marble chips by measuring the production of a gas?
You should have a conical flask with a gas syringe attached to it and held by a stand. Add dilute hydrochloric acid to the conical flask. Add marble chips into the conical flask and close the bung. Measure the volume of gas produced in a fixed time using a measuring cylinder or gas syringe.
-Investigate what happens when you change the size of the marble chips (Smaller chips=larger surface area=faster rate)
-Investigate what happens when you change the concentration of hydrochloric acid (greater concentration=greater no. of particles in a given volume=faster rate).
Mean rate of reaction (cm³/s) = total volume of gas produced/reaction time
Make a graph with volume of gas on the vertical axis and time on the horizontal axis. Plot the data with a curve of best fit.
How do you carry out the core practical to investigate changing the conditions in the reaction between sodium thiosulfate and hydrochloric acid by observing a colour change?
Add dilute sodium thiosulfate solution to a conical flask. Place the conical flask on a white tile which has a black cross marked on it. Then add dilute hydrochloric acid to the conical flask. Swirl the flask and start a stop clock.
Measure and record the temperature of the mixture. When the cross is no longer visible, record the time on the stop clock.
Repeat with different starting temperatures of sodium thiosulfate solution.
The rate of reaction increases as the temperature increases.
Calculate 1000/time for each temperature and plot a graph to show reaction rate (/s) on the vertical axis and temperature on the horizontal axis and plot the data with a curve of best fit.
Suggest a method for determining the rate of a reaction based on the amount of reactant used
Rate of reaction = amount of reactant used/time
If the product is a gas, you can carry out the reaction on a set of weighing scales and measure how much mass is lost
Can be measured either by mass in g/s or by volume in cm³/s
Suggest a method for determining the rate of a reaction based on the amount of product formed
Rate of reaction = amount of product formed/time
If the product is a gas you can measure the volume of gas produced in a gas syringe
Can be measured either by mass in g/s or by volume in cm³/s
Explain how reactions occur
-Chemical reactions only occur when the reacting particles collide with enough energy; the minimum amount of energy required is called activation energy.
-In order to increase the rate of a reaction you need to increase the frequency/energy of collisions so that more of them reach the activation energy.
-This can be done by: increasing temperature, pressure, concentration, surface area or by using a catalyst
Explain the effect on rate of reaction of a change in temperature
Increasing the temperature increase the rate of reaction as increasing temperature increases the kinetic energy of particles, so they collide more frequently and energetically.
Explain the effect on rate of reaction of a change in concentration
Increasing concentration of reacting solutions increases the rate of reaction, as it increases the number of particles in a given volume and so increases the frequency of collisions.
Explain the effect on rate of reaction of a change in surface area to volume ratio of a solid
Increasing the surface area of solid reactants increases the rate of reaction, as it increases the frequency of collisions so increases the rate of reaction.
Explain the effect on rate of reaction of a change in pressure
Increasing pressure in reacting gases increases the rate of reaction, as it increases the number of particles in a given volume so increases the frequency of collisions.
How do you interpret graphs of mass, volume or concentration of reactant or product against time?
-To find the rate of reaction graphically, draw tangents to curves and use the slope of the tangent as a measure of the rate of reaction.
-Gradient = rate of reaction, therefore the steeper a line the greater and increase/decrease in rate
-For a product you would expect the mass/volume/concentration to increase and for a reactant you would expect that to decrease.
Describe a catalyst
A substance that speeds up the rate of a reaction without altering the products of the reaction, being itself unchanged chemically and in mass at the end of the reaction
How does the addition of a catalyst increase the rate of a reaction in terms of activation energy?
-Catalysts decrease the activation energy, this increases the proportion of particles with energy to react, leading to more frequent successful collisions and so an increased rate of reaction.
-They lower the activation energy by providing a different pathway for a chemical reaction that has a lower activation energy.
Describe what enzymes are
Enzymes are biological catalysts/act as catalysts in biological systems
How are enzymes used in the production of alcoholic drinks?
Yeast is the enzyme used in the production of ethanol as it can directly ferment sugars into ethanol. Ethanol is in alcoholic drinks.
