9: Rate Equations Flashcards
Finding Rates from Graphs Orders of Reactions The Rate Determining Step The Arrhenius Equation
Give the formula for average rate of reaction.
Change in Time
Why does average rate of reaction decrease as the reaction proceeds?
Concentration of reactants decreases, so the probability of successful frequent collisions decreases.
Give the equation for finding rate from straight line graphs.
Gradient = Change in Y
—————–
Change in X
Give a general rate equation using A, B, M and N.
Rate = k [A]^m [B]^n
What do reaction orders show?
How concentration of each reactant affects rate.
For this rate equation, Rate = k [A]^m [B]^n, what would order with respect to A be when A changes but rate stays the same?
Zero.
For this rate equation, Rate = k [A]^m [B]^n, what would order with respect to A be when A doubles but rate stays the same?
Zero.
For this rate equation, Rate = k [A]^m [B]^n, what would order with respect to A be when A triples but rate stays the same?
Zero.
For this rate equation, Rate = k [A]^m [B]^n, what would order with respect to A be when A is proportional to rate?
1
For this rate equation, Rate = k [A]^m [B]^n, what would order with respect to A be when A doubles and rate doubles?
1
For this rate equation, Rate = k [A]^m [B]^n, what would order with respect to A be when A triples and rate triples?
1
For this rate equation, Rate = k [A]^m [B]^n, if rate is proportional to [A]^2, what will order with respect to A be?
2
For this rate equation, Rate = k [A]^m [B]^n, if order with respect to [A] is 2 and the concentration of A doubles, what will the new rate be?
Rate will square, so the new rate will be 4x faster.
For this rate equation, Rate = k [A]^m [B]^n, if order with respect to [A] is 2 and the concentration of A triples, what will the new rate be?
Rate will cube, so the new rate will be 9x faster.
What 2 things does the rate constant link together?
Rate of reaction to concentration of reactants.
The bigger the rate constant, the faster the…
Rate if reaction.
If the orders for each reactant are 1 and 2, what will the overall order of reaction be?
3
Will rate constant increase, decrease or stay the same if temperature increases?
Rate constant will increase as temperature increases.
How can we be sure that temperature increase has affected rate and nothing else?
Concentration or orders of reactants haven’t changed so an increase in K, which is affected by temperature, increases rate.
Draw a graph/describe the shape of a graph showing zero order and concentration.
Linear, similar to a negative correalation graph.
Draw a graph/describe the shape of a graph showing first order and concentration.
Reciprocal graph shape.
Draw a graph/describe the shape of a graph showing second order and concentration.
Exponential graph shape, but backwards.
Draw a graph/describe the shape of a graph showing zero order and rate.
A flat line, halfway up the centre of the graph.
Draw a graph/describe the shape of a graph showing first order and rate.
Linear, straight line. Like a positive correlation.
Draw a graph/describe the shape of a graph showing second order and rate.
Half a quadratic graph.
What is the rate determining step?
The ‘bottle neck’ in the reaction, where the slowest point in the reaction occurs.
The rate determining step can be used to find what about a chemical reaction?
The reaction mechanism.
How do we know if a reactant will have an impact on the rate of reaction?
The reactant will be present in the rate equation.
What does the Arrhenius equation show?
The Arrhenius equation shows how the rate constant varies with temperature and activation energy.
What are the units for activation energy?
Jmol-1
What will happen to K in the Arrhenius equation if activation energy gets bigger?
K gets smaller.
What happens to rate constant if temperature rises in the Arrhenius equation?
Why?
Rate constant increases.
This is because higher temperatures increase the kinetic energy of reactant particles so they are more likely to collide, increasing rate of reaction.
Give the Arrhenius equation rearranged for activation energy.
Ea = (In (A) - In (K)) x RT
Give the Arrhenius equation rearranged for temperature.
T = Ea
———————-
R (In (A) - In (K) )
