Rates Of Reaction Flashcards
(18 cards)
What is a zero order reaction?
Any number raised to the power of zero is one.
Therefore concentration has no influence on the rate
What is a 1st order reaction?
Its concentration is raised to the power of 1.
Rate directly proportional to concentration
Whatever you do to the concentration, the rate changes by the same factor.
What is a 2nd order reaction?
Rate proportional to the square of concentration
Whatever you do to the concentration, the rate changes by the same factor squared.
What would a concentration-time graph look like for a zero order reaction?
A straight line with a negative gradient.
Value of gradient is rate constant.
What would a concentration-time graph look like for a 1st order reaction?
A downward curve with a decreasing gradient over time.
The half-life for this can be used to determine the rate constant.
What would a concentration-time graph look like for a 2nd order reaction?
A downward curve steeper at the start than 1st order but tailing off more slowly.
What are the two methods to calculate the rate constant from a 1st order reaction?
Calculating the rate constant from the rate.
Calculating the rate constant from the half-life.
How would you use the rate to work out the rate constant for 1st order?
Draw a tangent to the curve on a concentration-time graph at a specific point . The gradient give you the rate of reaction.
Then sub this into the rate equation to work out the rate constant.
How could you use the half life to work out the rate constant for 1st order?
The exponential relationship for a constant half-life.
k=ln2 over half-life.
Much more accurate than drawing a tangent.
What does the rate-concentration graph look like for a zero order reaction?
Horizontal straight line with zero-gradient.
Y-intercept gives the rate constant.
Reaction rate does not change with increasing concentration.
What does the rate-concentration graph look like for a 1st order reaction?
A straight line through the origin.
Rate is directly proportional to concentration.
Rate constant is gradient of the graph.
What does the rate-concentration graph look like for a 2nd order reaction?
An upwards curve with a increasing gradient.
Cannot find rate constant directly from graph.
By plotting another graph of rate against concentration squared.
The result is a straight line through the origin.
Gradient of this line is equal to the rate constant.
What is a way to work out the initial rate of reaction?
Gradient of a tangent at time=0 on a concentration time graph.
What is a more efficient way of working out the initial rate of reaction?
A clock reaction is a type of initial rate experiment where you measure how long it takes for a visible change to occur (e.g. a colour change).
Then use initial rate =1 over time.
Why might the clock reaction not be that accurate?
The clock reaction assumes the rate remains constant until the endpoint, which may not be entirely accurate due to the reaction already progressing slightly before the observable change. Therefore the clock reaction is reasonably accurate provided that less than 15% of the reaction has occurred.
What factors affect the rate constant?
Explain how.
Increasing the temperature shifts the Boltzmann Distribution to the right, increasing the proportion of particles which exceed the activation energy.
As the temp increases, particles move faster and collide more frequently.
How do you calculate rate constants at different temperatures?
Using the Arrhenius Equation
K=A x e to the power of -activation energy/gas constant x temperature in K.
The exponential factor e to the power of etc.. represents the proportion of molecules which exceed activation energy.
A takes into account the frequency of collisions with the correct orientation.
How could you put this Arrhenius equation graphically?
Using ln k= - Activation energy/RT +ln A
Using y= mx + c
We know what the gradient, y-intercept is.
On graph plot ln K against 1 over t.
