Question 17 from 2012, regarding the direction of the reaction
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17. In the production of ammonia from natural gas as a raw material, the substances are assumed to be ideal gases. The conversion reaction of methane vapor is: CH4(g) + H2O(g) → CO(g) + 3H2(g); this is a reversible reaction. If the amount of water vapor is increased, in what direction will the reaction proceed? A: Changes in the direction of the reactants B: No effect C: Changes in the direction of the products D: Cannot be determined. An old question brought up again – it’s completely confusing. If it’s the addition of water vapor that increases the system pressure, then the change should occur in the direction that reduces pressure, that is, toward the reactants. But water vapor is also a reactant, doesn’t it move in the direction of the products as well? Is the answer D, that it cannot be determined?
I just listed the formulas; it seems that B has no impact
To determine the direction of the reaction, one needs to consider the changes in the concentrations of each component. In this case, if the volume remains constant, the addition of water vapor changes the concentration of water, while the concentrations of the other components remain unchanged; therefore, the reaction proceeds to the right. Since not all conditions are given, it is impossible to make a determination, so the answer is D
This question seems to lack complete information; from the perspective of pressure or concentration, it isn’t specified whether the volume remains constant
This question seems to lack complete information; from the perspective of pressure or concentration, it isn’t specified whether the volume remains constant
Approach 1: The production process takes place in a reactor, which is considered to have a constant volume； When water vapor is added, the equilibrium shifts in the direction of reduced pressure, that is, toward the reactants ； The addition of water vapor increases the concentration of the reactants; from a kinetic perspective, this leads to an increase in the rate of the forward reaction ； Correspondingly, the reverse reaction rate also increases ； But the ultimate result is that the reaction rate is greater than the forward reaction rate. Approach 2: The production process takes place in a reactor, considered to be at constant volume ； During the production process, pressure is generally controlled, with a constant pressure being taken into account ； At constant volume and constant pressure, adding more water vapor necessarily reduces methane or lowers the temperature ； Since the question doesn’t mention a reduction in methane, the system must show a tendency for its temperature to drop ； As the temperature decreases, the reaction necessarily shifts in the exothermic direction ； The forward reaction is endothermic, while the reverse reaction is exothermic ； Therefore, the balance also shifts to the left! !
This question should be understood as follows: Both methane and water vapor are reactants; by increasing the amount of reactants while keeping all other parameters unchanged, the reaction will definitely proceed in the direction of the forward reaction. In the case of methane, the reaction proceeds more completely, and in this sense, the reaction must go in the direction that results in the formation of products. That is, answer C is correct. The original poster is overcomplicating things.
For pure solids and pure liquids, increasing the amount of reactants does not change their concentration; in other words, the concentration of water remains unchanged. Therefore, from this perspective, the equilibrium does not shift； However, increasing the amount of water vapor raises the system pressure, causing the equilibrium to shift in the direction of reduced volume
Choose C: increasing the amount of reactants shifts the equilibrium to the right