Chapter 15: Chemical Equilibrium

The reaction X2(g) ⇌ 2 X(g) occurs in a closed reaction vessel at constant volume and temperature. Initially, the vessel contains only X2 at a pressure of 1.55 atm. After the reaction reaches equilibrium, the total pressure is 2.85 atm. What is the value of the equilibrium constant, Kp, for the reaction?

27

Consider the following reaction at chemical equilibrium: 2 SO2(g)+O2(g)⇌2 SO3(g) What is the effect of decreasing the volume of the reaction mixture? Increasing the volume of the reaction mixture?

Decreasing the volume causes the reaction to shift right. Increasing the volume causes the reaction to shift left.

An __________ is a gas which does not undergo chemical reactions under a set of given conditions. The Nobel gases often do react with many substances, and were historically referred to as the ________.

Inert gas; inert gases

The following reaction is endothermic: Heat +CaCO3(s) ⇌ CaO(s)+CO2(g) What is the effect of increasing the temperature of the reaction mixture? Decreasing the temperature?

Raising the temperature is equivalent to adding a reactant, causing the reactant to shift to the right. Lowering the temperature is equivalent to removing a reactant, causing the reaction to shift to the left.

The presence of a catalyst in an equilibrium reaction ____________.

Reduces the time required to reach equilibrium for the reaction

6: For the reaction 2 A(g) ⇌ B(g), the equilibrium constant is Kp = 0.76. A reaction mixture initially contains 2.0 atm of each gas (PA = 2.0 atm and PB = 2.0 atm). Which statement is true of the reaction mixture?

The reaction will proceed toward products.

N2(g)+3 H2(g)⇌2 NH3(g) What happens if we push down on the piston, lowering the volume and raising the pressure?

The reaction will shift to the right, 4 mol of gas particles are converted to 2 mol of gas particles.

Consider the following reaction at equilibrium: CaCO3(s)⇌CaO(s)+CO2(g) What is the effect of adding CO2 to the reaction mixture? What is the effect of adding CaCO3 ?

Adding CO2 increases the concentration of CO2 and causes the reaction to shift to the left. Adding addition CaCO3, however, does not increase the concentration of CaCO3 because CaCO3 is a solid and therefore has a constant concentration. Thus, adding CaCO3 has no effect on the position of the equilibrium.

2: The equilibrium constant for the reaction shown here is Kc = 1.0 × 103. A reaction mixture at equilibrium contains [A] = 1.0 × 10-3 M. What is the concentration of B in the mixture? A(g) ⇌ B(g)

1.0 M

Question 4Question 4: The reaction shown here has a Kp = 4.5 × 102 at 825 K. Find Kc for the reaction at this temperature. CH4(g) + CO2(g) ⇌ 2 CO(g) 2 H2(g)

6.428

Consider the following reaction in chemical equilibrium: 2 BrNO(g)⇌2 NO(g)+Br2(g) What is the effect of adding Br2 to the reaction mixture? What is the effect of adding BrNO?

Adding Br2 increases the concentration of Br2, causing a shift to the left (away from the Br2). Adding BrNO increases the concentration of BrNO, causing a shift to the right.

From the ideal gas law (PV=nRT0, we know that _____________ the numbers of moles of gas (n) results in a lower pressure (P).

Decreasing

If a chemical system is at equilibrium: ______________ the volume causes the reaction to shift in the direction that has the fewer moles of gas particles.

Decreasing

If a chemical system is at equilibrium: _______________ the concentration of one or more of the products (which makes Q < K) causes the reaction to shift to the right (in the direction of the products).

Decreasing

The following reaction is exothermic: 2 SO2(g)+O2(g) ⇌ 2 SO3(g) + Heat What is the effect of increasing the temperature of the reaction mixture? Decreasing the temperature?

If we increase the temperature, the reaction shifts to the left. If we decrease the temeprature the reaction move towards the right.

Pressure and volume are inversely related: A decrease in volume causes an ________ in pressure, and an increase in volume causes a __________ in pressure.

Increase; decrease

If a chemical system is at equilibrium: ____________ the volume causes the reaction to shift in the direction that has the greater number of moles of gas particles.

Increasing

If a chemical system is at equilibrium: Adding an ___________ to the mixture at a fixed volume has no effect on the equilibrium.

Inert gas

Decreasing the volume increases the pressure causing the reaction to the ____________________.

Side with fewer moles of gas, lower pressure

A change in___________ changes the actual value of the equilibrium constant K.

Temperature

Question 11Question 11: What is the effect of adding helium gas (at constant volume) to an equilibrium mixture of this reaction: CO(g) + Cl(g) ⇌ COCl2(g)

The reaction does not shift in either direction.

If a chemical system is at equilibrium: __________________ the concentration of one or more of the products (which makes Q > K) causes the reaction to shift to the left (in the direction of the reactants).

Increasing

If a chemical system is at equilibrium: _________________ the concentration of one or more of the reactants (which makes Q < K) causes the reaction to shift to the right (in the direction of the products).

Increasing

Consider the following reaction at chemical equilibrium: 2 KClO3(s)⇌2 KCl(s)+3 O2(g) What is the effect of decreasing the volume of the reaction mixture? Increasing the volume of the reaction mixture? Adding an inert gas at constant volume?

The chemical equation has 3 mol of gas on the right and zero mol of gas on the left. Decreasing the volume of the reaction mixture increases the pressure and causes the reaction to shift to the left (toward the side with fewer moles of gas particles). Increasing the volume of the reaction mixture decreases the pressure and causes the reaction to shift to the right (toward the side with more moles of gas particles). Adding an inert gas has no effect.

CaCO3(s) ⇌ CaO (s) + CO2 (g) What is the effect of removing carbon dioxide from the reaction mixture?

The reactions shifts right, the system will respond to minimize the change by increasing the concentration of CO2.

Consider the reaction between iodine gas and chlorine gas to form iodine monochloride. I2(g) + Cl2(g) ⇌ 2 ICl(g) Kp = 81.9 (at 298 K) A reaction mixture at 298 K initially contains PI2 = 0.25 atm and PCl2 = 0.25 atm. What is the partial pressure of iodine monochloride when the reaction reaches equilibrium?

0.41

Consider the reaction of A to form B. 2 A(g) ⇌ B(g) Kc = 1.8 × 10-5 (at 298 K) A reaction mixture at 298 K initially contains [A] = 0.50 M. What is the concentration of B when the reaction reaches equilibrium?

4.5 x 10^(-6)

If a chemical system is at equilibrium: When a reaction has ________________________ on both sides of the chemical equation, a change in volume produces no effect on the equilibrium.

An equal number of moles of gas

Question 9: The decomposition of NH4HS is endothermic: NH4HS(s) ⇌ NH3(g) + H2S(g) Which change to an equilibrium mixture of this reaction results in the formation of more H2S?

An increase in temperature

If a chemical system is at equilibrium: _______________ the concentration of one or more of the reactants (which makes Q > K) causes the reaction to shift to the left (in the direction of the reactants).

Decreasing

In an endothermic chemical reaction, heat is a reactant: ____________ the temperature causes an endothermic reaction to shift right (in the direction of the reactants); the value of the equilibrium constant decreases. _____________ the temperature causes an exothermic reaction to shift right (in the direction of the products); the value of the equilibrium constant increases.

Increasing; decreasing

In an exothermic chemical reaction, heat is a product: ____________ the temperature causes an exotehrmic reaction to shift left (in the direction of the reactants); the value of the equilibrium constant decreases. _____________ the temperature causes an exothermic reaction to shift right (in the direction of the products); the value of the equilibrium constant increases.

Increasing; decreasing

Question 1: What is the correct expression for the equilibrium constant (Kc) for the reaction between carbon and hydrogen gas to form methane shown here? C(s) + 2 H2(g) ⇌ CH4(g)

Kc = [CH4]/[H2]^2

Increasing the volume reduces the pressure, causing the reaction to shift to the _____________.

Side with more moles of gas, higher pressure

When a system at equilibrium is disturbed by a change in concentration or a change in volume, the equilibrium shifts to counter the change, but __________.

The equilibrium constant (K) does not change

What happens if, this time, we keep the volume the same but increase the pressure by adding an inert gas to the mixture?

There is no effect, ,and the reaction does not shift in either direction. Similarly, if the reaction has equal moles of gas particles on both sides of reaction, the effects of volume change on Q cancel each other out and there is no effect on the reaction (the reaction does not shift in either direction).

_____________ states that the chemical system responds to minimize the disturbance.

Le Chatelier's principle