S4 - Measuring rates of reaction
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How can the speed of a reaction be observed?
By how quickly the reactants are used up or how quickly the products are formed (easier to measure products formed)
What is the equation for working out the rate of an reaction?
Time
What are the three different ways of measuring the speed of a reaction?
• Precipitation • Change in mass (usually a gas given off) • The volume of the gas given off
How do you know if it is a precipitate reaction?
The solution becomes cloudy
How would you measure the speed of a reaction by the forming of a precipitate?
• Draw a cross on a piece of paper and put the conical glass with the solution directly above it • Observe the cross through the solution and time how long it takes for the cross to disappear (solution cloudy)
The quicker the cross disappears…
The quicker the reaction
What are the limitations of the precipitation method?
• Initial solution has to be see through - The results are very subjective
How can the change in mass be shown by the gas given off?
Using a mass balance, as the gas is released the mass disappearing is easily measured by the balance
The quicker the reading drops on the balance…
The faster the reaction
What are the advantages and disadvantages of using gas given off as a guide to the mass lost?
Advantage: • Results can be easily plotted on a rates of reaction graph • Very accurate as the mass balance is precise Disadvantage: - Releases gas straight into the room
How is the volume of a gas given off measured?
Using a gas syringe - the more gas given off during the reaction time interval, the faster the reaction
How do we know when the reaction has finished?
No more gas will be produced
What can be done with the results collected?
A graph of gas against time elapsed could be plotted to give a rate of reaction graph
Why are gas syringes very accurate?
They give volumes to the nearest millilitre *however you need to be careful because if the reaction is too vigorous, you can blow the plunger out of the end of the syringe!