Chem2 - Kinetics and Equilibria Flashcards
What is the activation energy on an enthalpy profile diagram?
It is the height of the peak between reactants and products
What is needed for a reaction to take place?
- collide in the right direction
- collide with equal to or above the activation energy
What is a Maxwell-Boltzmann distribution curve?
Its a curve which shows the different energies of the molecules within a sample of a gas, only so many have equal to or above the Ea
How does an increase in temperature affect a Maxwell-Boltzmann curve?
- shifts to the right
- peak a bit lower/flatter as same n# of molecules
- therefore more molecules have equal to or above Ea
How does an increase in pressure affect Maxwell-Boltzmann distribution curve?
- same curve but higher all over
- as more particles in sample
How does an increase in concentration affect Maxwell-Boltzmann distribution curve?
- same as increased pressure
- same as curve but higher all over
- more molecules in sample
Where is the average kinetic energy of a molecule on a Maxwell-Boltzmann curve?
Slightly to the right of the peak
What does a catalyst do?
It speeds up the rate of a reaction without itself being consumed or chemically changed
How does a catalyst have it’s effect?
It offers an alternative reaction pathway with a lower activation energy
How does a catalyst affect an enthalpy profile diagram?
It makes the height of the peak between reactants and products smaller
How does a catalyst affect a Maxwell-Boltzmann curve?
Moves activation energy to the left, so more molecules have equal to or higher than Ea
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What is the most probable energy of a molecule on a Maxwell-Boltzmann distribution curve?
Enthalpy at the peak
What is the rate equation of a reaction with reactants A and B, order of reaction 1 wrt A and 2 wrt B (1)
Rate of reaction = [A][B]^2
Define the term rate of reaction (1)
Change in concentration of reactants per unit time
How do you find out the order of each in the rate equation (when its not given)? (2)
Have no rate equation therefore can only work out using table of results!
~see how changing its concentration changes the rate of reaction
~if you x2 its conc and the rate doubles it has an order of 1, if x2 conc and rate quadruples it has order 2 (2^2 = 4), if x3 conc and rate multiplies by 9 then it has order 3 (3^2 = 9) etc
How do you work out the total order of reaction? (1)
~add up all the orders of reaction for the reactants in the rate of reaction equation
How do these factors affect k?
- > increase temperature
- > increase pressure (all gases)
- > increasing concentration of one of the reactants
- > adding a catalyst (4)
~temp increase, k increases
~pressure increase, k unchanged
~concentration increases, k unchanged
~k increases unless catalyst in rate equation in which case k is unchanged
