Block 3 Exam Questions Flashcards
What is the rate of a chemical reaction?
The change in concentration per unit time (mol L-1)
What is the instantaneous rate?
The rate at a particular time during the course of the reaction (and is the same as the slope of conc vs time)
What is the average rate?
- 1/a (delta A/ delta time)
What is the initial rate?
The instantaneous rate at the start of the reaction
Factors that affect rate of reaction?
- The nature of the reaction (eg metallic sodium with oxygen vs iron)
- Concentration of reactants
- Temperature
- Physical state of reactants
- Presence of catalysts
- Action of light
What is a rate law?
The relationship between the rate of a chemical reaction and the concentration of reactant(s)
What is a first order reaction?
The rate is proportional to the concentration of the reactant
Rate equal [A]
What is a second order reaction?
Where the rate is proportional to the square if the concentration
Rate equivalent to A^2
What are zero order reactions?
Where the rate is independent of concentration
What is a third order reaction ?
Where the rate is proportional to the cube of concentration
What is the rate constant?
The proportionality constant between rate and concentration (given by the symbol k)
Rate law for a first order reaction?
R= Ro e^(-kxt)
Which plots give a straight and curved line?
1st order = straight
2nd order = curved
Integrated rate law for a second order reaction?
1/R = 1/Ro + kt
What’s the half life and equation?
The time (in seconds) for the concentration of the reactant to fall to half its initial value (denoted by t1/2)
Half life value for first order reaction?
t 1/2 = ln 2/k
Half life equation for second order reaction?
t1/2 = 1/Ro k
What’s the Arrhenius equation?
The rate constant is related to temperature
K=Ae ^(Ea/RT)
What is the activation energy?
The amount of energy required to reach transition state
What’s a transition state/activated complex?
Distorted structure of reacting molecule when activation energy has been reached (high potential energy)
What is an elementary reaction?
Where reacting molecules must meet/collide to form/break new bonds
What are the classifications of elementary reactions?
Bimolecular elementary reaction (2 reactants)
Unimolecular elementary reaction (single molecule reacts by itself)
Termolecular elementary reaction (three reactants)
What are intermediate reactants?
Species that are products of the first step and reactants in the next etc
What is the rate limiting step?
The slowest step
What is a homogenous catalyst?
A catalyst that works in the same phase (gas, liquid, solid) as the reaction
What is a heterogenous catalyst?
A catalyst that works in a different phase than the reaction itself (eg a metal catalyst)
What is a parallel reaction?
Reactant A may react by two pathways yielding products B or C at different rates
What are explosions?
Characterised by reactions whose rates increases dramatically as the reaction proceeds
What is an oscillating reaction?
A reaction that doesn’t proceed smoothly, but rather generates products in bursts
