# Question 17.12: Predicting the Effect of a Change in Volume (Pressure) on th......

Predicting the Effect of a Change in Volume (Pressure) on the Equilibrium Position

Problem How would you change the volume for each of the following reactions to increase the yield of the product(s)?

(a) $CaCO_3(s) \xrightleftharpoons[] CaO(s) + CO_2(g)$           (b) $S(s) + 3F_2(g) \xrightleftharpoons[] SF_6(g)$
(c) $Cl_2(g) + I_2(g) \xrightleftharpoons[] 2ICl(g)$

Step-by-Step
The 'Blue Check Mark' means that this solution was answered by an expert.

Plan Whenever gases are present, a change in volume causes a change in concentration. For reactions in which the number of moles of gas changes, if the volume decreases (pressure increases), the equilibrium position shifts to lower the pressure by reducing the number of moles of gas. A volume increase (pressure decrease) has the opposite effect.

Solution (a) The only gas is the product $CO_2$. To make the system produce more molecules of gas, that is, more $CO_2$, we increase the volume (decrease the pressure).

(b) With 3 mol of gas on the left and only 1 mol on the right, we decrease the volume (increase the pressure) to form fewer molecules of gas and, thus, more $SF_6$.

(c) The number of moles of gas is the same on both sides of the equation, so a change in volume (pressure) will have no effect on the yield of ICl.

Check Let’s predict the relative values of $Q_c$ and $K_c$.
(a) $Q_c = [CO_2]$, so increasing the volume will make $Q_c < K_c$, and the system will yield more $CO_2$.
(b) $Q_c = [SF_6]/[F_2]^3$. Lowering the volume increases $[F_2]$ and $[SF_6]$ proportionately, but $Q_c$ decreases because of the exponent 3 in the denominator. To make $Q_c = K_c$ again, $[SF_6]$ must increase.
(c) $Q_c = [ICl]^2/[Cl_2][I_2]$. A change in volume (pressure) affects the numerator (2 mol) and denominator (2 mol) equally, so it will have no effect.

Question: 17.10

## Predicting Reaction Direction and Calculating Equilibrium Concentrations Problem The research and development unit of a chemical company is studying the reaction of CH4 and H2S, two components of natural gas: CH4(g) + 2H2S(g) ⥫⥬ CS2(g) + 4H2(g) In one experiment, 1.00 mol of CH4, 1.00 mol of CS2, ...

Plan (a) To find the direction, we convert the giv...
Question: 17.11

## Predicting the Effect of a Change in Concentration on the Equilibrium Position Problem To improve air quality and obtain a useful product, chemists often remove sulfur from coal and natural gas by treating the contaminant hydrogen sulfide with O2: 2H2S(g) + O2(g) ⥫⥬ 2S(s) + 2H2O(g) What happens to ...

Plan We write the reaction quotient to see how [la...
Question: 17.14

## Determining Equilibrium Parameters from Molecular Scenes Problem For the reaction, X(g) + Y2(g) ⥫⥬ XY(g) + Y(g) ΔH > 0 the following molecular scenes depict different reaction mixtures (X is green, Y is purple): (a) If K = 2 at the temperature of the reaction, which scene represents the mixture at ...

Plan (a) We are given the balanced equation and K ...
Question: 17.13

## Predicting the Effect of a Change in Temperature on the Equilibrium Position Problem How does an increase in temperature affect the equilibrium concentration of the underlined substance and K for each of the following reactions? (a) CaO(s) + H2O(l) ⥫⥬ Ca(OH)2(aq) ΔH° = −82 kJ (b) CaCO3(s) ⥫⥬ CaO(s) ...

Plan We write each equation to show heat as a reac...
Question: 17.6

## Calculating Kc from Concentration Data Problem In order to study hydrogen halide decomposition, a researcher fills an evacuated 2.00-L flask with 0.200 mol of HI gas and allows the reaction to proceed at 453°C: 2HI(g) ⥫⥬ H2(g) + I2(g) At equilibrium, [HI] = 0.078 M. Calculate Kc. ...

Plan To calculate $K_c$, we need the ...
Question: 17.3

## Converting Between Kc and Kp Problem Ammonium hydrosulfide decomposes to ammonia and hydrogen sulfide gases. Find Kc for the decomposition reaction: NH4SH(s) ⥫⥬ NH3(g) + H2S(g) Kp = 0.19 (at 218°C) ...

Plan We know $K_p$ (0.19), so to conv...
Question: 17.8

## Determining Equilibrium Concentrations from Initial Concentrations and Kc Problem Fuel engineers use the extent of the change from CO and H2O to CO2 and H2 to regulate the proportions of synthetic fuel mixtures. If 0.250 mol of CO gas and 0.250 mol of H2O gas are placed in a 125-mL flask at 900 K, ...

Plan We have to find the “composition” of the equi...
Question: 17.7

## Determining Equilibrium Concentrations from Kc Problem In a study of the conversion of methane to other fuels, a chemical engineer mixes gaseous CH4 and H2O in a 0.32-L flask at 1200 K. At equilibrium, the flask contains 0.028 mol of CO, 0.084 mol of H2, and 0.045 mol of CH4. What is [H2O] at ...

Plan First, we write the balanced equation and the...
Question: 17.2