NH4HS(s) NH3(g) + H2S(g) ∆H_ = +93 kilojoules
The equilibrium above is established by placing solid NH4HS in an evacuated container at 25°C. At equilibrium, some solid NH4HS remains in the container. Predict and explain each of the following.
(a) The effect on the equilibrium partial pressure of NH3 gas when additional solid NH4HS is introduced into the container
b) The effect on the equilibrium partial pressure of NH3 gas when additional solid H2S is introduced into the container
c) The effect on the mass of solid NH4HS present when the volume of the container is decreased
(d) The effect on the mass of solid NH4HS present when the temperature is increased.
You need an arrow. How do you which are the products and which the reactants?
a) If there is solid NH4HS initially, adding more solid NH4HS will not cause the equilibrium to change; therefore, no effect.
b) Confusing. There is NO solid H2S present initially; therefore, how can ADDITIONAL solid H2S be added.
c)Volume is decreased, pressure is increased. Equilibrium changes to the side with the smaller number of moles; therefore, the equilibrium will shift to the left and NH3 will be decreased, H2S is decreased, mass of NH4HS is increased.
d) This is an endothermic reaction which can be written as
NH4HS(s) + heat ==> NH3(g) + H2S(g)
Adding heat will shift the equilibrium to the right; therefore, the mass of the NH4HS will decrease.
(a) When additional solid NH4HS is introduced into the container, according to Le Chatelier's principle, the equilibrium will shift to the right to counteract the change. This means that more NH3 gas and H2S gas will be produced in order to maintain equilibrium. Therefore, the partial pressure of NH3 gas will increase.
(b) Similarly, when additional solid H2S is introduced into the container, the equilibrium will again shift to the right to counteract the change. More NH3 gas and H2S gas will be produced to restore equilibrium. Therefore, the partial pressure of NH3 gas will increase.
(c) If the volume of the container is decreased, the equilibrium will shift to the side with fewer gas molecules to reduce the pressure. In this case, that corresponds to the left side, where solid NH4HS is present. Therefore, the mass of solid NH4HS present will increase.
(d) When the temperature is increased, according to Le Chatelier's principle, the equilibrium will shift in the direction that absorbs heat to counteract the change. In this case, the forward reaction is endothermic (∆H = +93 kilojoules), meaning it absorbs heat. Therefore, the equilibrium will shift to the right to produce more NH3 gas and H2S gas in order to consume the excess heat. As a result, the mass of solid NH4HS present will decrease.
(a) The effect on the equilibrium partial pressure of NH3 gas when additional solid NH4HS is introduced into the container:
When additional solid NH4HS is introduced into the container, it will cause an increase in the concentration of NH4HS in the system. According to Le Chatelier's principle, when the concentration of a reactant in a system is increased, the system will shift in the direction that consumes that reactant, in order to establish a new equilibrium. In this case, since the forward reaction consumes NH4HS and produces NH3 gas, the system will shift to the right (towards the products) to consume the additional NH4HS.
As a result, the concentration of NH3 gas will increase. According to the ideal gas law, an increase in concentration will result in an increase in partial pressure. Therefore, the equilibrium partial pressure of NH3 gas will increase when additional solid NH4HS is introduced into the container.
(b) The effect on the equilibrium partial pressure of NH3 gas when additional solid H2S is introduced into the container:
When additional solid H2S is introduced into the container, it will cause an increase in the concentration of H2S in the system. According to Le Chatelier's principle, when the concentration of a reactant in a system is increased, the system will shift in the direction that consumes that reactant, in order to establish a new equilibrium. In this case, since the forward reaction consumes H2S and produces NH3 gas, the system will shift to the right (towards the products) to consume the additional H2S.
As a result, the concentration of NH3 gas will increase. According to the ideal gas law, an increase in concentration will result in an increase in partial pressure. Therefore, the equilibrium partial pressure of NH3 gas will increase when additional solid H2S is introduced into the container.
(c) The effect on the mass of solid NH4HS present when the volume of the container is decreased:
When the volume of the container is decreased, the pressure of the system will increase. According to Le Chatelier's principle, when the pressure of a system is increased, the system will shift in the direction that reduces the number of moles of gas, in order to establish a new equilibrium. In this case, since the forward reaction produces NH3 gas, the system will shift to the left (towards the reactants) to reduce the number of moles of gas.
As a result, more NH4HS will be formed from NH3 gas and H2S gas, leading to an increase in the mass of solid NH4HS present in the container.
(d) The effect on the mass of solid NH4HS present when the temperature is increased:
When the temperature is increased, it will disrupt the existing equilibrium. According to Le Chatelier's principle, when the temperature of a system is increased, the system will shift in the direction that consumes heat, in order to establish a new equilibrium. In this case, since the forward reaction is exothermic (releases heat), the system will shift to the right (towards the products) to consume the heat.
As a result, more NH3 gas and H2S gas will be formed from the solid NH4HS, leading to a decrease in the mass of solid NH4HS present in the container.