IB Chemistry Topic 6/16

How is initial rate of a reaction calculated

Draw a tangent at t = 0

It is where the rate is greatest due to having the highest concentration of reactants

How can rate of reaction be calculated by volume of gas produced

Collecting the gas and measuring the change in volume.

This can be used using a gas syringe or an inverted burette, measuring water displacement

A data logger can also be used

How can rate of reaction be calculated by change in mass

Perform the experiment on a balance, if the mass change is significant, if not it will not work.

How can rate of reaction be calculated by change in transmission of light

If one of the reactants is coloured, so absorbed in the visible light spectrum. A colorimeter or spectrophotometer can be used which passes light of a specific wavelength through the studied solution, and measured the intensity of light transmitted by the components.

What does the Maxwell Boltzmann distribution curve show

The particles in a gas at a particular temperature show a range in their values of kinetic energy which is expressed in the curve.

What does the “successfulness” of a reaction depend on

The energy of the collision

The geometry of the collision

How does particle size affect the rate of reaction

Decreasing particle size increases rate of reaction

This is because increased surface area increases contact and probability of a collision

What is the rate equation

Rate = k[A]^m[B]^n, where k is the rate constant, [A] and [B] are the concentrations of reactants, and m and n are the reaction orders with respect to A and B

What is the overall order of a reaction

The sum of all individual orders

What are the units of k in a zero order reaction

mol dm^-3 s ^-1

What are the units of k in a first order reaction

s^-1

What are the units of k in a second order reaction

mol^-1 dm³ s ^-1

What are the units of k in a third order reaction

mol^-2 dm⁶ s ^-1

What does the graph of a zero order reaction look like

Conc-time graph = straight diagonal line showing constant rate

rate-conc graph = horizontal line

What does the graph of a first order reaction look like

Conc-time graph = curve showing rate decreasing with conc

Rate-conc graph = straight line passing through the origin with gradient k

What does the graph of a second order reaction look like

Conc-time graph = steeper at start than 1st order and levels off more but is still a negative curve

Rate-conc graph = parabola, rate is initially zero.

How can we deduce that a reaction is zero order

If changing the concentration of A has no effect on the rate, A is zero order

How can we deduce that a reaction is first order

If changing the concentration of A directly proportionally changes the rate. eg. doubling conc of A doubles rate of reaction then A is first order

How can we deduce that a reaction is second order

If changing the concentration of A lead to a square in rate. Eg. if doubling the conc of A quadruples the rate. Then A is second order

What is the rate determining step

The slowest step in a reaction mechanism, it determines the overall rate of reaction.

How do we determine a rate expression from a reaction mechanism

If there is a coefficient before a reactant then that is of that order. eg. 2A means A to the second order.

How do zero order reactants affect the rate determining step

They don’t as they don’t take part in the step

What is the Arrhenius equation

Arrhenius equation relates rate constant with temperature for chemical reactions. It is k = A * e^(-Ea/RT)."

k = rate constant

A = Arrhenius constant

Ea = Activation energy

T = temperature

R = gas constant (8.31)