Rate Equations - Determining Orders of Reactions Graphically (A-Level Chemistry)
Determining Order of Reaction Graphically
Using graphs to determine order of reaction
We can determine the order of reaction graphically, by analysing what happens in an investigation.
The concentration of the reactant can be analysed over time and a graph plotted of concentration versus time.
Tangents to the curve are drawn at different points on the graph, at different concentrations. This is shown by lines A,B and C.
The gradient of the tangents are calculated. This gives the rate at particular concentrations.
A graph of rate vs concentration is plotted.
The shape of this graph enables us to determine the order of reaction with respect to the reactant being investigated.
The diagrams below summarise all the possibilities.
Zero Order:
We can see that concentration doesn’t affect the rate of reaction
- Concentration vs time graph – A straight line is obtained
- Rate vs concentration graph – A horizontal line is produced
First Order:
As concentration increases, rate increases too, it is a proportional relationship.
- Concentration vs time graph – A curve with a decreasing gradient is produced
- Rate vs concentration graph – A straight line, through the origin with a positive gradient.
Second Order:
As concentration increases, rate increases too, in the form of a curved graph
A curve is produced with both the concentration vs time and rate vs concentration graph.
A rate equation is a mathematical expression that relates the rate of a chemical reaction to the concentrations of the reactants. It allows us to understand the relationship between the reaction rate and the reactants, which is crucial for predicting and controlling the outcome of chemical reactions in A-Level Chemistry.
The order of a reaction can be determined graphically by plotting the rate of the reaction against the concentration of the reactants. The slope of the line that results from this plot can be used to determine the order of the reaction. If the slope of the line is proportional to the concentration of one reactant, then the reaction is first-order with respect to that reactant. If the slope of the line is proportional to the square of the concentration of one reactant, then the reaction is second-order with respect to that reactant.
The rate constant of a reaction is directly proportional to the rate of the reaction and is a measure of the speed of the reaction. The relationship between the rate constant and the order of the reaction is given by the rate equation, which is derived from the rate law. If the reaction is first-order, the rate constant is proportional to the rate of the reaction. If the reaction is second-order, the rate constant is proportional to the square of the concentration of the reactants.
Sure! Let’s consider the reaction between hydrogen peroxide (H2O2) and potassium permanganate (KMnO4) to form oxygen gas (O2) and manganese dioxide (MnO2). To determine the order of the reaction graphically, we can plot the concentration of the reactants against the rate of the reaction. If the slope of the line is proportional to the concentration of H2O2, then the reaction is first-order with respect to H2O2. If the slope of the line is proportional to the square of the concentration of H2O2, then the reaction is second-order with respect to H2O2.
The order of a reaction determines the relationship between the rate of the reaction and the concentrations of the reactants. A higher-order reaction will have a faster rate of reaction when the concentrations of the reactants are high, while a lower-order reaction will have a slower rate of reaction even when the concentrations of the reactants are high. This is because the rate of a higher-order reaction is more sensitive to changes in the concentrations of the reactants, while the rate of a lower-order reaction is less sensitive to these changes.
Determining the order of a reaction is important because it allows us to understand the relationship between the rate of the reaction and the concentrations of the reactants. This information is crucial for predicting and controlling the outcome of chemical reactions, such as optimizing reaction conditions for maximum yield or minimizing waste. Additionally, the order of a reaction can also provide insight into the underlying mechanisms of the reaction, which can be useful for developing new and more efficient reaction pathways.
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