OCR A-Level Chemistry: Chapter 18 - Rates of Reactions
This flashcard set defines reaction rate and its units, then explores how changes in reactant concentration affect rate depending on reaction order—zero, first, or second—providing a clear understanding of kinetic behavior.
What is a reaction’s rate?
The change in concentration per second.
Key Terms
What is a reaction’s rate?
The change in concentration per second.
What is rate measured in?
Mol dm^-3 s^-1
In a chemical reaction, if A is zero order, what effect would be seen if [A] is doubled?
Reaction rate would not change.
In a chemical reaction, if A is first order, what effect would be seen if [A] is doubled?
Reaction rate would double.
In a chemical reaction, if A is second order, what effect would be seen if [A] is doubled?
Reaction rate would quadruple.
How is the reaction rate at a specific time worked out using a concentration against time graph?
At the set time, draw a tangent to the curve and measure the gradient to get the rate.
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| Term | Definition |
|---|---|
What is a reaction’s rate? | The change in concentration per second. |
What is rate measured in? | Mol dm^-3 s^-1 |
In a chemical reaction, if A is zero order, what effect would be seen if [A] is doubled? | Reaction rate would not change. |
In a chemical reaction, if A is first order, what effect would be seen if [A] is doubled? | Reaction rate would double. |
In a chemical reaction, if A is second order, what effect would be seen if [A] is doubled? | Reaction rate would quadruple. |
How is the reaction rate at a specific time worked out using a concentration against time graph? | At the set time, draw a tangent to the curve and measure the gradient to get the rate. |
If there are two reactants, A and B, what would be the rate equation? | rate = k x [A]^m x [B]^n |
What is initial rate? | The instantaneous rate at the beginning of an experiment when t=0. |
In a concentration time graph, and a rate time graph, what would zero order look like? | Concentration time - linear to 0 concentration Rate time - Horizontal line |
In a concentration time graph, and a rate time graph, what would first order look like? |
Rate time - Linear proportional |
In a concentration time graph, and a rate time graph, what would second order look like? | Concentration time - steeper curve Rate time - proportional to x^2 |
What are the two ways of continuous monitoring when a gas is produced? | Gas collection Mass loss |
What is a way of utilising light to monitor rate? | Using a colourimeter. Measuring the amount of light absorbed by a solution. |
What is half life? | The time taken for half of a reactant to be used up. |
In a concentration time graph, how can you deduce whether the reactant is first or second order? | Measure multiple half lives. |
If the rate is only affected by one reactant, which is first order, what is another way of determining the rate constant? | k = ln|2| / t(1/2) |
What is a reaction mechanism? | A series of steps that, together, make up the overall reaction. |
What is the rate determining step? | The slowest step in the reaction mechanism of a multi-step reaction. |
Why does temperature affect the rate constant? | Increasing the temperature, increases rate of reaction and thus rate constant. |
| k = A x e^(-E(a)/RT) |
What is the logarithmic form of the Arrhenius equation? | ln|k| = -E(a)/RT + ln|A| |
What can the log form of the Arrhenius equation be modelled as? | A straight line graph in y=mx + c ln|k| is y -E(a)/R is m 1/T is x ln|A| is c |