Chemical Industry 5: Half Lives & Determing Orders from Experiments Flashcards
What are the 2 main methods of following the rate of a reaction
- Initial rates method
2. Continuous rates method ( progress curve)
Describe how an initial rates method works
- Do several reactions starting with different concentrations and measure the inititial rate of each one by
- measuring time taken for an easily recognisable event to happen very early on in a reaction Eg. Volume of gas produced / colour change
( time how long it takes to reach a specific point early in the reaction)
Describe how continuous rates method works
Measure the rate at several points during one reaction
take samples of the mixture at intervals
How do you work out rate from initial rates method
Initial rate = 1/ time taken
How do you work our rate from continuous method
Rate = gradient of graph ( concentration-time)
What kind of graph can you draw from initial rates method
Rate against concentration graph
What kind of graph can you draw from continuous method
Concentration against time graph
Learn what the graphs of 0, 1st & 2nd order for rate-concentration graph look like
Look in notes
Learn what the graphs of 0, 1st & 2nd order for concentration-time graph look like
Look in notes
For a continuous method graphs ( concentration-time) what is a way of proving that its is first order
Half life method
- take a why value and half it and recourd time taken to half
- repeat again with different y value and if time taken to half is the same then rate of reaction is first order
Definition of half life
Half life of a reaction is the time taken for half of the reactant to be used up
What is special about the half life if the rate of reaction is first order
- the time for half the reactant to be used is always the same
- half life of a first order reaction is independent of the concentration = each half life the same length
