Rates Of Reaction Flashcards
What are 5 experimental methods of obtaining rate data?
- Mass change
- Volume of gas evolved
- Titration
- Colorimetry
- pH meter
How is rate calculated on a graph?
- Gradient of the line change in y/change in x
- Draw a tangent where curve meets specific point if curved
Rate reaction equation
Rate = k[A]^a [B]^b
What are units for rate?
mol-1dm-3s-1
What does the orders of reaction tell us?
Tells us how the concentration of the substance affects the rate
Orders of reaction
Zero - no change
First- Rate Doubles
Second- Rate quadruples
What happens to the rate constant if you increase the temperature
The particles have more kinetic energy and they collide more often, this increases the rate. The larger the value of ‘k’ the faster the rate of reaction.
Different between rate-concentration graph and concentration time graph
- R-C are created by knowing the rate.
- The rate is found by taking the gradient at various points on a C-T graph
What is half life?
Half life is the time it takes for half of the reactant to be used up
What does it mean for the rate constant if there is a constant half life?
It is 1st order
Half life equation
- k = ln (2) / t1/2
- t1/2 = ln (2)/ k
How to word comparing experiment questions
Comparing Experiments X and Y, [A] is (x) order with respect to [A]
Rate determining step
The slowest step in a multi-step reaction (e.g putting a cake in the oven)
What does the orders indicate about the rate determining step?
- The orders indicate the number of molecules of each substance involved
What does the arrehnius equation tell us?
Shows how k and temperature are related exponentially and links activated energy
What happens to the rate constant as the activation energy gets smaller
The rate constant gets bigger because the rate of reaction increases. More particles have enough energy to react when they collide.
Arrhenius plot to find out activation energy and Arrhenius constant
LnK = -Ea/R x 1/T + lnA
y = mx + c
What do we assume about the rate of reaction in clock experiments?
The rate of reaction remains constant so the average rate is same as the initial rate
What do we assume about the temperature in clock experiments?
Remains consatnt
What do we assume about the concentration in clock experiments?
The concentration of reactant doesn’t change significantly during the time period of the reaction
What do we assume about the reaction in clock experiments?
Reaction has not proceeded too far when the end point is seen
What does the reactants that appear in rate equation tell us about the rate determining step?
Reactants that appear in the rate equation affect the rate of reaction, therefore these reactants must appear in the rate determining step.
