3.5 Chemical Kinetics Flashcards
What is the collision theory
Reactants must collide at the correct orientation and with significant energy
Factors that affect rate of reaction
Concentration
Pressure
Surface area
Temperature
Catalyst
How does a catalyst work
Lowers the activation energy needed for a reaction to begin
What is order of reaction
The power to which we have to raise the concentration to fit the rate equation
Some methods used to measure rate of reaction
• measure gas volume at constant pressure
• measure gas pressure at constant volume
• measure change in mass
• use of colorimetry
• sampling and quenching
What is the overall order of reaction
The sum of the powers of the concentration terms in the rate equation
How must orders be found
Experimentally
What is k
Rate constant
What affects k
Temperature and catalyst
What is the unit for rate
Moldm-3s-1
What to look for when working out rate data
Find 2 sets of data where only 1 concentration changes
What is the reaction mechanism
The steps that must occur during a chemical reaction
What is the rate determining step
The rate of the slowest step that limits the overall rate of reaction
What does it mean if the concentration of a reactant appears in the rate equation
The reactants or something derived from it takes place in the rate determining step
State the Arrhenius equation
K= Ae^-Ea/RT
Units for activation energy in the Arrhenius equation is
Jmol-1
What is the effect of a catalyst on the Arrhenius equation
It will lower the activation energy
This will cause the value of e to increase and so the value of K will increase
What can entropy be described as
A measure of disorder
Or
The amount of randomness in a system
Or
The dispersal of energy
What is the symbol for entropy
S
Greater entropy means
More disorder
Put solid, liquid, gas in order of increasing entropy
Solid<liquid<gas
How to calculate the entropy change from absolute entropy values
/\S = Sfinal - Sinitial
What is standard entropy
The entropy contents of one mole of that substance under standard conditions
Units for stanard entropy
Jk-1mol-1
What does Gibbs free energy do
Combines entropy and enthalpy to decide if a reaction is feasible or not
How to calculate gibs free energy
/\G=/\H - T/\S
What does it mean if gibbs free energy is negative
The reaction is feasible and can occur spontaneously
What does it mean is gibbs free energy is positive
At that temperature the reaction is not feasible and cannot occur spontaneously
What is the value of /\G at the temperature that the reaction begins to be possible
0
How to calculate the temperature that a reaction begins to be possible
T = /\H / /\S
What is the value of /\G when the system is at equilibrium
0
