Rate = change in concentration/ change in time. [A] is shorthand for ‘concentration of A’.

Rate of Reaction: The change in concentration of a reactant or product per unit time.

Units: Usually it is mol dm-3 s-1. -1 in superscript means ‘per’ or ‘divide’.

Orders of Reaction: The order with respect to a reactant is the power to which the

concentration of the reactant is raised in the rate equation. Common orders are…

Zero Order: When concentration of reactant has no effect on rate. Rate ∝ [A]0 . Any number

raised to power zero is 1. Know zero order if reactant is in excess as conc doesn’t change much.

First Order: Rate ∝ [A]1 . If concentration A x3, reaction rate increased by x31

= x3.

Second Order: Rate ∝ [A]2

. If concentration of A x3, reaction rate increased by x32

= x9.

Rate Equation: Rate = k [A]m

[B]n

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.

M and n superscript are order of reaction. Multiply A and B.

If question asks to ‘write the rate equation’- write equation above but omit zero order reactants

completely and the 1

for first order. Include state symbols.

Write 7.0 x 10n

for standard form and not just 7.

Overall Order: Overall order gives overall effect on concentrations of all reactants of rate of

reactions. Overall order = sum of orders with respect to each reactant = m + n from equation

above.

Units of Rate Constant: Make k the subject. Remember rate has different units to concentration.

Cancel top and bottom. Move any units in bottom to top by inversing sign in powers. Put positive

indices before negative in units.

Multiply when power outside bracket OR add powers e.g. (moldm-3 )(moldm-3) = mol2

dm-6

.

K = rate/ [A]m

[B]n

– CO x2, rate of reaction also x2 so reaction is 1st order with respect to CO.

– Make sure to say which experiments. In table ignore a reactant if zero order, even if values

change when comparing.

– Write rate equation once found out all orders, with chemical symbols. Even if not asked to.

– Remember to write the units of k rate constant. K is just a number- a constant.

– Only reactants involved in rate equation and power is not the balancing number but the

order.

– Zero order wrt to reactant when rate does not change with concentration.

– If something zero order, still prove it is zero order.

Experimental Results: When comparing effect of concentrations, measure rate for all at initial

rate when t = 0.

Change standard form into normal numbers to make it less confusing.

Or just leave out standard form bit in calculator but adjust any standard form differences if

needed.

Look out for standard form differences.