5.1.1 How Fast? Flashcards
What is the rate of reaction?
- change in concentration of a reactant or product per unit time
What is the order?
- with respect to a reactant is the power to which the concentration of the reactant is raised in the rate equation
What is the overall order?
- the sum of the individual orders
What is the rate constant?
- k
- the constant that links the rate of reaction with the concentrations of the reactants raised to the powers of their orders in the rate equation
What is zero order?
- rate is unaffected by changing the concentration of A
- not present in rate equation
What is first order?
- rate is directly proportional to the concentration
What is second order?
- the change in rate will be equal to the change in concentration squared
What is the rate equation?
- rate = k[A][B][C]
What is the shape of concentration-rate graphs for different orders?
- 0 order - straight line horizontally
- 1 order - directly proportional
- 2 order - exponential (as conc x2, rate x4)
What is the shape of concentration-time graphs for different concentrations?
- 0 order - graph decreases at constant rate (straight line)
- 1 order - concentration halves at equal time intervals (constant half life)
- 2 order - concentration decreases rapidly (half life increases)
What is the rate determining step of a reaction?
- the slowest step in a reaction mechanism of a multi step reaction
What does each component in the Arrhenius equation mean?
- k = rate constant
- A = pre-exponential factor (same units as k)
- Ea = activation energy Jmol-1
- R = universal gas constant (8.314) Jmol-1k-1
- T = temperature in Kelvin
What is the effect of temperature on rate constants?
- as temperature increases, the rate constant increases and the rate of reaction increases
What is half-life?
- the time taken for the initial concentration of the reactants to decrease by half
- t|1/2
What is the half-life for a first order reaction?
- the half life is constant throughout the reaction
What experimental techniques can be used to obtain rate data for reactions?
- measuring change in reactant mass or concentration over time
- measuring change in product mass or concentration over time
How can mass change produce rate data?
- if gas if produced, mass of mixture will decrease
- plotting mass-time graph and drawing a tangent to curve can find initial r of r
How can volume of gas obtain rate data?
- measuring volume of gas produced and plotting graph of volume against time
- gas cylinder used to collect gas
How can titration be used to obtain rate data?
- small samples of reaction mixture can be removed at regular intervals throughout a reaction
- samples can be titrated to determine the conc of a given reactant or product
- a concentration-time graph can then be plotted
How can colorimetry be used to obtain rate data?
- amount of light absorbed by colorimeter is proportional to concentration of coloured species
- calibration curve can be generated (colorimeter measures absorbance of solutions with known concentrations)
Describe the iodination of propanone (iodine clock)
CH3COCH3 + I2 -> CH3COCH2I + H+ + I-
- initial solution brown due to iodine present
- as iodine is used up, solution changes from brown to orange to yellow and finally to colourless
- the concentration of iodine can be found by continually taking samples of reaction mixture and measuring absorbance using a colorimeter
What is the relationship between the rate constant (k) and constant half life?
- k = ln 2 / t 1/2
