In this lesson, we will learn:

- How data from chemical reactions can be presented in graphs.
- How to interpret graphs showing data from chemical reactions.

__Notes:__- After an investigation into the rate of a reaction, graphing the results to find the rate can be done in a number of ways, depending on what you measure and how you represent it.
- The most important thing to do when interpreting
__ANY__graph is to read the axes – what are they measuring? What does a change in x or a change in y represent?__Time should ALWAYS be displayed on the x-axis__. - This is very important when reading reaction rate graphs or graphing them yourself – you should choose how to display your data carefully.
- Reaction rate graphs often have very distinct
__curves__or__shapes__which are strong evidence of a change in rate. However, these are very__dependent on what is being displayed__on the graph! - On a graph of product formed over time:
__A flat curve (where gradient = 0) shows the reaction has stopped__. Because your y-axis is measuring product formed, if it doesn't change, it is showing that more product has formed since the last data point, therefore the reaction has stopped and the__reaction rate is zero__. This normally happens after some time to show all the available produce has been made.- The curve rising (y value increasing) shows more product is being formed – the reaction is still occurring.
- The steeper the gradient, the faster the reaction rate (greater $\frac{dy}{dx}$ )
- Product formed over time graphs
__do not show declines!__Once a product is formed, it does not revert back to reactants. These graphs should not decline – if they do, there could be a mistake in your measurements. - On a graph of change in reactant mass over time:
__A flat curve (where gradient = 0) shows the reaction has stopped__. As above, this normally happens after some time to show the- The general trend will be the y axis dropping – a declining curve, because reactant mass is going to be decreasing as products are formed.
- Again, the steeper the gradient, the faster the reaction rate (greater $\frac{dy}{dx}$ ) because the amount of reactant mass is decreasing more per unit time.
- In summary, these graphs are similar to the 'product formed over time' graphs except the curve generally drops instead of increases!
- On a graph of rate over time, the shape of the curve will have a different meaning:
__A flat curve means the reaction rate is constant__. Unless y = 0, the y axis staying constant shows that the reaction is still occurring at the same rate it was when measured at the last data point.- Any change in y is showing a change in rate – the reaction is speeding up or slowing down.
__The curve dropping to zero (the y-axis 0) shows the reaction has stopped.__