Calculating Equilibrium Constants
Be able to calculate Q and predict which direction a reaction will proceed. Be able to calculate K eq and predict where the equilibrium position will be. A few other summary statements about K eq. K eq is independent of the concentration of reactants and products. Examine Table 14.1. The actual amounts of. Calculate the Keq for the following reaction: N2O4(g) 2NO2(g) If N2O2 = 0.0185 mol/L and NO2 = 0.0627 mol/L. If the way I wrote the problem looks confusing can someone just tell me how to calculate Keq and maybe I can figure out the rest. Thank you for your answers in advance.
Sep 24, 2016 Find Kb for ammonia: This would simply be the given Keq for the reaction. Kb is just the Keq of a specific type of reaction between a base and water. Ammonia is a weak base. Find Ka of conjugate acid. This is would equal the Keq of the reverse reaction. The Keq of the reverse reaction is the reciprocal of the the forward reaction. A variation of Type 1 problems is when you are given the Keq and all the equilibrium concentrations except one and you are asked to calculate that one. The solution for this type of problem is simply writing out the Keq expression, filling in what you know and solving for the unknown. Read through this example: At 200°C, the Keq for the.
We need to know two things in order to calculate the numeric value of the equilibrium constant:
- the balanced equation for the reaction system, including the physical states of each species. From this the equilibrium expression for calculating Kc or Kp is derived.
- the equilibrium concentrations or pressures of each species that occurs in the equilibrium expression, or enough information to determine them. These values are substitued into the equilibrium expression and the value of the equilibrium constant is then calculated.
- Write the equilibrium expression for the reaction.
- Determine the molar concentrations or partial pressures of each species involved.
- Subsititute into the equilibrium expression and solve for K.
c , for the system shown, if 0.1908 moles of CO
How To Calculate Keq From Delta G
2, 0.0908 moles of H2, 0.0092 moles of CO, and 0.0092 moles of H2O vapor were present in a 2.00 L reaction vessel were present at equilibrium. CO + H2O' height =34 src='EquilibriumArt/CalcKexample1.gif' width=288 NOSAVE>
- Write the equlibrium expression for the reaction system.
- Since Kc is being determined, check to see if the given equilibrium amounts are expressed in moles per liter (molarity). In this example they are not; conversion of each is requried.
[CO2] = 0.1908 mol CO2/2.00 L = 0.0954 M
[H2] = 0.0454 M
[CO] = 0.0046 M
[H2O] = 0.0046 M - Substitute each concentration into the equilibrium expression and calculate the value of the equilibrium constant.
Calculating K from Initial Amounts and One Known Equilibrium Amount
- Write the equilibrium expression for the reaction.
- Determine the molar concentrations or partial pressures of each species involved.
- Determine all equilibrium concentrations or partial pressures using an ICE chart.
- Substitute into the equilibrium expression and solve for K
N2 + 2 H2O' height=32 src='EquilibriumArt/CalcKexample2.gif' width=326 >
- Write the equilibrium expression for the reaction.
- Check to see if the amounts are expressed in moles per liter (molarity) since Kc is being . In this example they are.
- Create an ICE chart that expresses the initial concentration, the change in concentration, and the equilibrium concentration for each species in the reaction. From the chart you can determine the changes in the concentrations of each species and the equilibrium concentrations. From the example, we start with the folowing information.
Initial Concentration (M) | ||||
Change in Concentration (M) | - 2 x | + x | + 2 x | |
Equilibrium Concentration (M) |
The change in concentration of the NO was (0.062 M - 0.100M) = - 0.038 M. Thus -2 x = - 0.038 and x = 0.019. Note: the negative sign indicates a decreasing concentration, not a negative concentration. The changes in the other species must agree with the stoichiometry dictated by the balance equation. The hydrogen will also change by - 0.038 M, while the nitrogen will increase by + 0.019 M and the water will increase by + 0.038 M. From these changes we can complete the chart to find the equilibrium concentrations for each species.
Initial Concentration (M) | ||||
Change in Concentration (M) | ||||
Equilibrium Concentration (M) |
- Substitute the equilibrium concentrations into the equilibrium expression and solve for Kc.
Calculating K from Known Initial Amounts and the Known Change in Amount of One of the Species
- Write the equilibrium expression for the reaction.
- Determine the molar concentrations or partial pressures of each species involved.
- Determine all equilibrium concentrations or partial pressures using an ICE chart.
- Substitute into the equilibrium expression and solve for K.
How To Calculate Keq Given Delta G
2 NO2' height =29 src='EquilibriumArt/CalcKexample3.gif' width=181 NOSAVE>
- Write the equilibrium expression to find Kp.
How To Calculate Keq Of A Reaction
- Check to see that the given amounts are measured in appropriate pressure units since Kp is to be . In this example they are (atmospheres).
- Create an ICE chart and calculate the changes in pressure and equilibrium pressures for each species.
Initial Pressure (atm) | ||
Change in Pressure (atm) | ||
Equilibrium Pressure (atm) |
- Substitute the equilibrium pressures into the expression for Kp and solve for Kp.