5.1 Rates, equilibrium and pH (Unfinished)

What is rate of reaction defined in physical chemistry?

the change in concentration of a substance in unit time

What is the rate of reaction usual unit?

Its usual unit is mol dm^-3s ^-1

When a graph of concentration of reactant is plotted vs time what is the gradient of the curve

the gradient of the curve is the rate of reaction.

what is the initial rate?

The initial rate is the rate at the start of the reaction where it is fastest

How can reaction rates be calculated from graphs?

Reaction rates can be calculated from graphs of concentration of reactants or products, by drawing a tangent to the curve (at different times) and calculating the gradient of the tangent.

what does the rate equation relate to

The rate equation relates mathematically the rate of reaction to the concentration of the reactants.

For the following reaction:

aA + bB —> products

what is the generalised rate equation?

• r is used as symbol for rate

• The unit of r is usually mol dm^-3 s ^-1

• m, n are called reaction orders

• The square brackets [A] means the concentration of A (unit mol dm^-3 )

• k is called the rate constant

Explain reaction orders

• m, n are called reaction orders

• Orders are usually integers 0,1,2

• 0 means the reaction is zero order with respect to that reactant

• 1 means first order

• 2 means second order

• the orders have nothing to do with the stoichiometric coefficients in the balanced equation.

• They are worked out experimentally.

• The total order for a reaction is worked out by adding all the individual orders together (m+n)

What do graphs of initial rate against concentration show?

the different orders

How may have the initial rate been calculated when looking at graphs of initial rate against concentration

from taking gradients from concentration/time graphs.

For a rate concentration graph to show the order of a particular reactant what must happen

the concentration of that reactant must be varied whilst the concentrations of the other reactants should be kept constant.

What is the equation for the rate reaction for zero order and explanation

• the concentration of A has no effect on the rate of reaction

• r = k[A]⁰ = k

What is the equation for the rate reaction for first order and explanation

• the rate of reaction is directly proportional to the concentration of A

• r = k[A]¹

What is the equation for the rate reaction for second order and explanation

• the rate of reaction is proportional to the concentration of A squared

• r = k[A]²