Rate equations

• reaction rate

  change in the amount of reactants or products per unit time
• measuring rate of reaction

  pH

  lost mass

  gas released

  colour change
• rate from straight line

  gradient
• rate from curve

  tangent
• rate equation

  $k[A]^m[B]^n$ for A + B -> C + D
• units of rate

  $moldm^{-3}s^{-1}$
• m and n are the orders of reaction with respect to reactants A and B and k is the rate constant

  The orders m and n are restricted to the values 0, 1, and 2
• The rate constant k varies with temperature

  $k=$$Ae^{-E_a/RT}$

  A is a constant, known as the Arrhenius constant, Ea is the activation energy and T is the temperature in K
• Working out reaction orders from graphs

  Find the gradient (which is the rate) at various points along the concentration-time graph

  the points and join them up with a line or smooth curve.

  
• rate-determining step

  if a reactant appears in the rate equation, it must affect the rate. So this reactant, or something derived from it, must be in the rate-determining step. If a reactant doesn’t appear in the rate equation, then it won’t be involved in the rate-determining step and neither will anything derived from it