18.1 Orders, Rate equations, and Rate constants Flashcards
Chapter 18 - Rates of reactions
How are reaction rates measured?
Observing the changes in quantities of reactants or products over time.
Give two rate equations.
rate = quantity reacted or produced / time
rate = change in concentration / change in time
What is the most common unit of rate?
mol dm-3 s-1.
(concentration measured in moldm-3 and time measured in seconds).
What is the shorthand notation used for the concentration of reactant A?
[A]
units: mol dm-3
What is the rate of reaction proportional to?
The concentration of a particular reactant raised to a power.
rate ∝ [A]^n
What is the order of reaction?
The power for that reactant.
What is zero order?
rate = ∝ [A]^0
- Any number raised to the power of zero is 1.
- Concentration does not influence the rate.
- NO EFFECT
What is first order?
rate ∝ [A]^1
- If concentration of A doubles, rate doubles
- If concentration of A triples, rate triples.
- SAME EFFECT
What is second order?
rate ∝ [A]^2
- If concentration of A doubles, rate quadruples.
- If concentration of A triples, rate increases by x9.
- SQUARED EFFECT
What is the rate equation?
The mathematical relationship between the concentrations of the reactants and the reaction rate.
State the rate equation.
rate = k [A]^p [B]^m [C]^n
k - rate constant
p,m,n - order of reaction with respect to A,B,C
A,B,C - concentrations
What is the rate constant?
A proportionality constant that converts between the rate of reaction and concentration and orders.
What is the overall order of reaction?
The overall effect of the concentrations of all reactants on the rate of reaction.
How is the overall order of reaction calculated?
overall order = sum of orders with respect to each reactant.
What is the rate units for an overall order of zero?
mol dm-3 s-1
What is the rate units for an overall order of one?
s-1
What is the rate units for an overall order of two?
mol-1 dm3 s-1
What is initial rate?
The instantaneous rate at the beginning of an experiment when t=0.
How must the orders of reactions be determined experimentally?
Monitoring how a physical quantity changes over time. Order cannot be found directly from a chemical equation.
