[petstar21]

I get the formula R= K [A]
but i dont understand how to formulate that. i heard that you square one of the reactants but what about coefficients in an equation, pleaaase help~

[Astrokel]

hey, try this 

http://www.chemicalforums.com/index.php?topic=25958.0

[cliverlong]

Having just looked at this topic.

In addition to the link I would add

Rate is defined as change of concentration divided by time

The rate equation looks a bit like equilibrium constant equation because of the concentration terms  - don't be deceived - they are significantly different expressions

The equlibrium equation includes concentrations of reactants and products.

The rate equation only includes concentration of REACTANTS - repeat many times

The rate equation powers of concentration of REACTANTS - are not connected with the number of moles of reactant in balanced equation - repeat many times

Most questions are provide data on INITIAL rate and INITIAL concentration of reactants - and then vary the concentration of one species - so you can determine the rate order of each species.

The curves are in two groups

Curve type 1: Concentration of reactant versus time

Curve type 2: Rate versus (initial) concentration of reactant

Don't mix the graph types up. Learn the shapes and be able to explain for NO REACTION (rarely given), zero order, first order, second order for both graph types.

Rate half-life is easiest to understand on the first-order concentration - time graph. Then extend from there to other orders.

With a little bit of "head maths"  and some thinking, you should be able to relate the shape of a concentration-time graph to the rate-concentration graph for each order. Remember rate = - gradient of the concentration-time graph


Clive