rate equations and Kp Flashcards
Define rate of reaction:
The change in concentration of a substrate in unit time
What are the units of rate of reaction?
mol dm^-3 s^-1
What are the three factors that affect rate of reaction?
Temperature, concentration of reagents, presence of a catalyst
At a fixed temperature, where is the rate of reaction at its greatest?
At the start of a reaction, because the concentration of the reactants is greatest
How is rate affected as the reaction proceeds?
The concentration of the reactants decreases and therefore the rate falls
What is the general rate equation?
Rate= k [A]^m [B]^n
What is k in the context of rate equations?
k is the rate constant. k varies depending on the type of reaction taking place
What is order?
Order is the power to which the concentration term is raised in the rate equation
How does temperature affect the rate constant?
Rate constant varies exponentially with temperature
Describe the relationship between concentration of reactant and rate in a zero order reaction:
Rate of reaction is unaffected by concentration of the reactant, and rate will be constant throughout the reaction
What are the units of k in a zero order reaction?
mol dm^-3 s^-1
What is the relationship between concentration of reactant and rate if the reaction is 1st order?
If concentration of a reactant changes by a factor, the rate will change by the same factor
What are the units of k in a first order reaction?
s^-1
What is the relationship between concentration of reactant and rate if the reaction is 2nd order?
If concentration of a reactant increases by a factor then the rate of reaction will increase by the square of that factor
What are the units of k in a second order reaction?
mol^-1 dm^3 s^-1
How is rate of reaction found using a graph?
The rate at a particular time is found by measuring the gradient at that time
What is the initial rate?
The rate at the start of reaction when the initial concentrations of the reagents are known.
How can the rate equation be determined?
By studying the effect on the initial rate of changes in the initial concentrations of reagents
What is the rate determining step?
The slowest step in a reaction involving multiple steps. Species in the rate equation must be found in the rate determining step
How is a catalyst represented in a reaction?
The catalyst will appear in the rate equation, but not in the overall chemical equation
What does the Arrhenius equation link?
Links rate constant, the temperature and the activation energy
What are the two Arrhenius equations?
k=A e^(-Ea/RT)
lnk=-Ea/RT + lnA
What is Kp?
Kp is the equilibrium constant for a system at equilibrium where all reactants and products are in the gaseous state
How is Kp calculated?
First calculate mole fraction:
moles of each reactant/ total moles of gas in the mixture
Multiply mole fraction by the total pressure of the reaction to find partial pressure
Kp= (pC)^c / (pA)^a (pB)^b
