15.3. ICE Charts and Kc Calculation in Equilibrium Chemistry

Overview of Ice Charts and Equilibrium Calculations

Introduction to Ice Charts

  • Ice charts are essential tools for calculating equilibrium concentrations in chemical reactions.

  • The acronym ICE stands for:

    • I: Initial concentrations

    • C: Change in concentrations

    • E: Equilibrium concentrations

  • Importance of accurately calculating equilibrium to understand reaction dynamics.

Examples and Calculations

Reaction Considered

  • Reaction:
    CO(g)+2H<em>2(g)→CH</em>3OH(g)CO(g) + 2 H<em>2(g) \rightarrow CH</em>3OH(g)

  • Temperature for reaction: 780 degrees (not directly used in calculations).

  • Initial concentrations provided:

    • [CO]initial=0.5extM[CO]_{initial} = 0.5 ext{ M}

    • [H<em>2]</em>initial=1extM[H<em>2]</em>{initial} = 1 ext{ M}

  • Given equilibrium concentration of CO:

    • [CO]equilibrium=0.15extM[CO]_{equilibrium} = 0.15 ext{ M}

Constructing the ICE Chart

  • Prepare the ICE chart below the balanced equation:

    • Initial row:

    • [CO]=0.5[CO] = 0.5

    • [H2]=1[H_2] = 1

    • [CH3OH]=0[CH_3OH] = 0

    • Change row:

    • For CO, the change is negative due to consumption of reactants: −x-x

    • For H2, since the coefficient is 2: −2x-2x

    • For CH3OH (product), since the coefficient is 1: +x+x

    • Equilibrium row:

    • [CO]=0.5−x[CO] = 0.5 - x

    • [H2]=1−2x[H_2] = 1 - 2x

    • [CH3OH]=x[CH_3OH] = x

Solving for x

  • Known value to find x is from the equilibrium concentration of CO:

    • 0.5−x=0.150.5 - x = 0.15

  • Solving for x:

    • x=0.5−0.15=0.35x = 0.5 - 0.15 = 0.35

Update Change and Equilibrium Values

  • Repeat the substitution for the changes in concentrations:

    • For H2:

    • [H2]=1−2(0.35)=1−0.70=0.30[H_2] = 1 - 2(0.35) = 1 - 0.70 = 0.30

    • For CH3OH:

    • [CH3OH]=0+0.35=0.35[CH_3OH] = 0 + 0.35 = 0.35

  • Thus, updated equilibrium concentrations:

    • [CO]=0.15[CO] = 0.15

    • [H2]=0.30[H_2] = 0.30

    • [CH3OH]=0.35[CH_3OH] = 0.35

Calculation of Equilibrium Constant Kc

Expression for Kc

  • The expression for the equilibrium constant Kc derived from the balanced equation:

    • K<em>c=[CH</em>3OH][CO]1[H2]2K<em>c = \frac{[CH</em>3OH]}{[CO]^1[H_2]^2}

  • Substituting the equilibrium concentrations into this expression:

    • Kc=0.35(0.15)(0.302)K_c = \frac{0.35}{(0.15)(0.30^2)}

Computing the Value of Kc

  • Performing the calculation:

    • Value of Kc results in:

    • Kc=26K_c = 26

    • Interpretation of Kc:

    • Kc > 1 indicates that products are favored in the equilibrium state.

Homework Assignment

  • Homework example requires similar calculations for another reaction not covered in detail during the session.

  • Must include:

    • ICE chart construction

    • Calculation of Kc using given initial and equilibrium concentrations.

  • Must be submitted in written form by Thursday.

Important Notes and Reminders

  • Remember to include coefficients as exponents when writing the equilibrium constant expression.

  • Emphasis on proper techniques for conducting experiments and ensuring correct handling of lab equipment.

Conclusion

  • Understanding ICE charts is crucial for equilibrium calculations.

  • Next session will build on this foundation with more complex examples.