Chemical Kinetics

Chemical Kinetics

The Rate of Reaction is measured by the change in molarity over time.  By convention, we use the decreasing molarity of the reactants instead of the increasing molarity of the products.  The rate of a reaction depends upon many factors: the number of molecules, how fast they are moving, how they are colliding, …  Because of this, reaction rate is not linear, it is an exponential decay.

Instantaneous rate is the rate at a specific moment in time.  It is determined by the slope of the tangent line to the curve.  The only way to determine this without calculus is to graph the data and manually approximate a tangent line.

Average rate is the rate between 2 specific times.  It is determined by the slope of the line between the 2 times on the curve.  You do not need an actually graph the data to determine average rate, just use the (time, molarity) as (x,y) and determine the slope by ∆x/∆y.

The formula for the rate law for an equation is always    rate=k[reactant]^order

The power or order of the reaction for each reactant must be determined from experimental data.  The total order for a reaction is equal to the sum of the orders for each reactant. 

• This method requires that a reaction be run several times.
• The initial concentrations of the reactants are varied.
• The reaction rate is measured just after the reactants are mixed.
• Eliminates the effect of the reverse reaction.