Rate Graphs
- Data recorded in rate studies is used toplot graphsto calculate the rate of a reaction
- 时间通常是策划x-axiswith theconcentrationof the reactant or product on they-axis
- A number of measurements should be taken to provide a complete set of data
- If the relationship between the factor being measured and the amount produced isdirectly proportional(i.e. if the concentration of a reactant doubles the rate also doubles) then the resulting graph will be astraight line graphgoing through the origin
- Thegradientof the line is equal to theinitial rateofreactionand thesteeperthe gradient of the line then thefasterthe rate of reaction
Initial Rate Graphs
An initial rate graph for the formation of a product shows a straight line with a positive correlation starting from the origin
- A reaction rate graph based on measurements of a reactant being used up will have a negative correlation
An initial rate graph for a reactant shows a straight line with a negative correlation starting from the y-axis
Rate Graphs Until Completion
- Plotting a graph until the completion of the reaction shows how the rate changes with time
- The concentration of a reactant or product may be plotted against time and will produce one of the following curves:
The concentration of a reactant or product against time
- Over time the rate of reaction slows as the reactants are being used up so the line becomes less steep and eventually becomeshorizontal, indicating the reaction has finished
- Often it is more practical to measure a property like mass of volume against time
- 您可以绘制多个运行th的一个变量e same graph making it easier to see how the variable influences the rate
- For Example, plotting the effect of concentration on a reaction between acid and marble chips:
This graph shows how the mass/volume of a product changes over time for a high concentration and a low concentration
- Drawing atangentto the slope allows you to show the gradient at any point on the curve
- The volume of a gaseous product would increase to a maximum over time, so the line levels out indicating the reaction is over
- Since the volume and mass would be proportional, this could also be a graph of mass of product versus time
Exam Tip
Make sure you can interpret reaction graphs and use them to describe how a reaction proceeds as questions do come up on this topic.
