Effect of temperature

  • When the temperature of a reaction is increased generally the reaction rate increases

  • A 100C rise in temperature approximately doubles the rate

    • Rate of reaction = k[A]m[B]n

  • Since the concentrations will not be changed by the temperature the only thing that can be affected is the rate constant

  • Is there an equation that links temperature to rate constant?

    • Yes, the Arrhenius equation

  • Arrhenius equation

A = Arrhenius constant (sometimes called frequency factor or pre-exponential factor). It has the same units as the rate constant

The Arrhenius constant makes allowance for the frequency of successful collisions, allowing for collision geometry and energy requirements

H2(g) + I2(g) → 2HI(g)

Temp/K

k / dm3mol-1s-1

500

4.3 × 10-7

600

4.4 × 10-4

700

6.3 × 10-2

800

2.6

  • The Arrhenius equation can be rearranged to give:-

    In k = -EA/RT + ln A

  • A graph of k versus (1/T) will give a gradient of (-EA/R) and an intercept of ln A.

ln k

1/T / k-1

-14.66

2.00 × 10-3

-7.73

1.67 × 10-3

-2.76

1.43 × 10-3

0.96

1.25 × 10-3