Approaching Equilibrium:

H2(g) + I2(g) 2 HI (g)

Historical backgroundThe simulation with water is useful because it lets us see the changes in reactant and product concentrations in an exaggerated manner.  Unfortunately, we can't see molecules transferring from one side of a reaction to the other.  However, we can have the computer run a simulation of a reaction for us.

Run simulation
Click to start the simulation

 This computer simulation of the gas phase hydrogen - iodine - hydrogen iodide equilibrium will let you see how the concentrations would change in a real reaction.  Set the initial conditions as follows:
  • [H2] = 0.0 M
  • [I2]  = 0.0 M
  • [HI] = 0.4 M
  • Temperature = 356 ºC

then press the simulation's [Show Graph] button.

Help using the simulation
Click for help

Note especially how the rate of the forward and reverse reactions change with time.  In the simulation, the length of the colored arrows in the equilibrium symbol are used to indicate the forward and reverse reaction rates.  A longer arrow indicates a faster rate.

You can also use the simulation to verify the meaning of the equation coefficients.

Analysis:

Try running the simulation at these conditions.  Note carefully what happens as the conditions change.

Analyze results

Click on this icon to check your understanding of the results

Set the temperature = 356 °C and measure the results at the following concentrations:

Note: the first trial is the conditions described above, so you should have already finished it.

Trial 1 Trial 2 Trial 3
  • H2] = 0.0 M
  • [I2]  = 0.0 M
  • [HI] = 0.4 M
  • [H2] = 0.2 M
  • [I2]   = 0.2 M
  • [HI]  = 0.0 M
  • [H2]  = 0.1 M
  • [I2]    = 0.1 M
  • [HI]   = 0.4 M
 

Set the following concentrations: [H2] = 0.0 M, [I2] = 0.0 M, and [HI] = 0.4 M, and then vary the temperature.

Trial 1: Temperature = 400 °C Trial 2: Temperature = 350 °C Trial 3: Temperature = 300 °C