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Rate Equations
AQA A Level Chemistry
Question | Answer |
---|---|
How can the rate of reaction be measured? Give 3 different examples | Measure volume of gas produced, Monitor the change in mass, time taken for colour to change |
What is the unit of rate of reaction? | mol dm-3 s-1 |
Write a rate equation for a reaction that is first order with respect to reactant A and 2nd order with reactant B. | r = k [A] [B]2 |
Write a rate equation for a reaction that is first order for X and first order for Y | r = k [X] [Y] |
For a reaction that is second order with respect to reactant Y what would happen to the rate if the concetration is tripled? | Rate would increase by 9 x |
For a reaction that is second order with respect to reactant A, what will happen to the rate of reaction if the concentration of A is doubled? | It will be quadrupled. |
Explain what the order of a particular reactant is in terms of the particles of that reactant in the mechanism of the reaction | The order of a particular reactant is the number of particles of that reactant that participate before or during the rate determining step. |
What is the order of a particular reactant in the rate equation of a particular reactant | "The power to which a concentration is raised in the rate equation |
" What is the overall order of a chemical reaction. | "The sum of all the individual orders in the rate equation. |
" If a reaction is zero order with respect to a reactant Z what is the effect on the rate of a reaction of increasing the the concentration of Z | No effect. |
What is the unit of the rate constant k in this rate equation? rate = k [A] | s-1 |
What is the unit of the rate constant k in this rate equation? rate = k [P] [C] | mol-1 dm3 s-1 |
What is the unit of the rate constant k in this rate equation?rate = k [D]2 [B] | "mol-2 dm6 s-1 |
" How does a catalyst increase the rate of a reactant? | "Catalysts provide an alternative reaction pathway with a lower Activation Energy. Decreasing the Activation Energy means that more particles will have sufficient energy to overcome the energy barrier and react |
" How is the initial rate calculated from a graph of conc v time | Draw a tangent at t=0 and calculate the gradient |
How is the rate at 30 sec calculated from a graph of conc v time | Draw a tangent at t=30 and calculate the gradient |
In a continous rate method you must have one reactant largely in excess. Explain why? | The reactant that has a large excess will have a very small change in concentration so is effectively kept constant |
How could you confirm the order of a reactant graphically | plot a graph of rate v conc and if it’s a straight line it is order 1 wrt reactant. If not plot rate v conc2 for order 2 etc.. |
What order is a horizontal line when a graph of rate v conc is plotted | zero order |
What order is a straight line graph of rate v conc | Order 1 |
What order is a straight line graph of rate v conc2 | Order 2 |
How do you convert Temp in degrees to Kelvin | add 273 |
The Arrhenius equation is lnK = lnA- Ea/RT. Describe how a graph that could be plotted from a number of values of K(rate constant) and T (Temperature in K) to determine the value of activation energy Ea | lnK should be plotted on the y axis, 1/T on the x axis then the gradient is -Ea/R |
Calculate the Ea if A= 2.7x10^11 and k = 0,.00450mol-1dm3s-1 and T=683K using lnK = lnA- Ea/RT. Give your answer to 3 sig figs | 180kjmol-1 |
If a reaction is zero order with respect to a reactant Z where must Z be in the mechanism of the reaction? | After the Rate Determining Step |
What is meant by rate determining step | The slowest step in the mechanism of a reaction |
Why are catalysts in the rate equation but are not in the chemical equation? | Catalyst are in the mechanism for the reaction but are regenerated so are not found in the chemical equation |