The document discusses reaction rate graphs and how to analyze them: - Graph A shows a faster reaction rate than Graph B because it produces more product in less time as seen by its steeper slope. - Graph C shows a reaction that used more reactants than Graph B because it produced more total product over the same time period. - Reaction rates can be compared by calculating the slope of the linear portion of the graphs or measuring the time taken to produce a set amount of product. - Graph B shows the reaction slowing down due to lack of reactants as the slope decreases over time. Graph C shows the reaction fully stopped as no more product is being formed. Graph A shows the fastest reaction rate based on its stee

1. Instructions: Use this slide show to consider some key questions about reaction rate graphs Click on the next slide button to see the answers and an explanation about each question Understanding Reaction Rate Graphs

2. Which experiment shows the fastest reaction rate, a or b ? time (s) Volume gas / cm 3 b a 1 2 3 4 5 6 7 8 9 10 12 13 14 15 16 17 18 19 20 21 22 11 5 10 15 20 25

3. Which experiment shows the fastest reaction rate, a or b ? time (s) Volume gas / cm 3 b a 1 2 3 4 5 6 7 8 9 10 12 13 14 15 16 17 18 19 20 21 22 11 Answer… Experiment ‘a’ The gradient of experiment ‘a’ is always steeper than experiment ‘b’ Compare the amount of gas produced after 2s experiment ‘a’ has produced 10cm 3 of gas experiment ‘b’ has produced 15cm 3 of gas … to produce more gas experiment a must be reacting faster 5 10 15 20 25

4. An experiment was run using the same reaction, but with different amounts of reactants. Which experiment used more reactants, b or c ? time (s) Volume gas / cm 3 b c 1 2 3 4 5 6 7 8 9 10 12 13 14 15 16 17 18 19 20 21 22 11 5 10 15 20 25

5. An experiment was run using the same reaction, but with different amounts of reactants. Which experiment used more reactants, b or c ? time (s) Volume gas / cm 3 b c 1 2 3 4 5 6 7 8 9 10 12 13 14 15 16 17 18 19 20 21 22 11 5 10 15 20 25 Answer… Experiment ‘c’ Remember, the reactants react to produce the products The more reactant you put in, the more products will be formed Experiment b eventually produced approximately 24cm 3 of gas, whereas experiment c produced 30cm 3 of gas

6. List two ways that you could compare the rates of these two reactions time (s) Volume gas / cm 3 1 2 3 4 5 6 7 8 9 10 12 13 14 15 16 17 18 19 20 21 22 11 5 10 15 20 25 b a

7. List two ways that you could compare the rates of these two reactions time (s) Volume gas / cm 3 1 2 3 4 5 6 7 8 9 10 12 13 14 15 16 17 18 19 20 21 22 11 5 10 15 20 25 b a Approach 1: Work out the rates by taking the gradients The first part of a rate graph is always a straight line The gradient of the line is equal to the reaction rate To calculate the gradient you need to: pick a point on the straight part of the line read the values for this point on the y (vertical) and x (horizontal) axes, in this case: y=10cm 3 and x=2s divide y by x, or in this case: Volume of gas time check the equation used to calculate the rate of a reaction in the section ‘Measuring rates of reaction ’ above you should notice when you calculate the gradient of the line, you are actually divided the change in product (gas) by the time take taken – which is how you calculate a rate !!!

8. List two ways that you could compare the rates of these two reactions time (s) Volume gas / cm 3 1 2 3 4 5 6 7 8 9 10 12 13 14 15 16 17 18 19 20 21 22 11 5 10 15 20 25 b a Approach 2: Time how long is takes to produce a set amount of product Before the line becomes flat, a reaction with a faster reaction rate will produce a set amount of product quicker Pick an amount of product that is on the straight part of each graph Then read the time is took each reaction to produce this set amount of product The less time is took to produce this amount of product, the faster the reaction Whilst this method does not give you an actual reaction rate, it is a valid way of comparing how fast different reactions are happening

9. time (s) Volume gas / cm 3 b a 1 2 3 4 5 6 7 8 9 10 12 13 14 15 16 17 18 19 20 21 22 11 5 10 15 20 25 Which part of the reaction rate graph shows the reaction slowing down because the reactants are running out the reaction having stopped The reaction happening at the fastest rate c

10. time (s) Volume gas / cm 3 b a 1 2 3 4 5 6 7 8 9 10 12 13 14 15 16 17 18 19 20 21 22 11 5 10 15 20 25 Which part of the reaction rate graph shows the reaction slowing down because the reactants are running out the reaction having stopped The reaction happening at the fastest rate c Answers: b shows the reaction slowing down because the reactants are running out – the gradient of the curve is getting less, so the reaction rate is slowing down. Put another way, less products are being formed as each second goes by, so the reaction is slowing down c shows the reaction having stopped. No more products are being formed – the amount of gas is staying the same a show the reaction happening at the fastest rate. The gradient is the steepest at this point