Topic 7.1-7.8 - Rates of reaction

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.

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.

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

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

-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

Increasing the temperature increase the rate of reaction as increasing temperature increases the kinetic energy of particles, so they collide more frequently and energetically.

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.

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.

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.

-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 an 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.

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

-Catalysts decrease the activation energy by providing a different pathway for a chemical reaction that has a lower 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.

Enzymes are biological catalysts/act as catalysts in biological systems

Yeast is the enzyme used in the production of ethanol as it can directly ferment sugars into ethanol. Ethanol is in alcoholic drinks.