Question

Chemistry help please

Answer 1

Answer:

The reaction isn't yet at equilibrium. The overall reaction will continue to move in the direction of the products.

Assumption: this system is currently at $\rm 900^{\circ}C$.

Explanation:

One way to tell whether a system is at its equilibrium is to compare its reaction quotient $Q$ with the equilibrium constant $K_c$ of the reaction.

The equation for $Q$ is quite similar to that for $K_c$. The difference between the two is that $K_c$ requires equilibrium concentrations, while $Q$ can be calculated even when the system is on its way to equilibrium.

For this reaction,

$\displaystyle Q = \rm \frac{[CS_2]\cdot [H_2]^{4}}{[CH_4]\cdot [H_2S]^{2}}$.

Given these concentrations,

$\displaystyle Q = \rm \frac{[CS_2]\cdot [H_2]^{4}}{[CH_4]\cdot [H_2S]^{2}} =\frac{1.51\times (1.08)^{4}}{1.15\times (1.20)^{2}} \approx 1.72$.

The question states that at $\rm 900^{\circ}C$, $K_c = 3.59$. Assume that currently this system is also at $\rm 900^{\circ}C$. (The two temperatures need to be the same since the value of $K_c$ depends on the temperature.)

It turns out that $Q = K_c$. What does this mean?

• First, the system isn't at equilibrium.
• Second, if there's no external changes, the system will continue to move towards the equilibrium. Temperature might change. However, eventually $Q$ will be equal to $K_c$, and the system will achieve equilibrium.

In which direction will the system move? At this moment, $Q < K_c$. As time proceeds, the value of $Q$ will increase so that it could become equal to $K_c$. Recall that $Q$ is fraction.  

$\displaystyle Q = \rm \frac{[CS_2]\cdot [H_2]^{4}}{[CH_4]\cdot [H_2S]^{2}}$

When the value of $Q$ increases, either its numerator becomes larger or its denominator becomes smaller, or both will happen at the same time. However,

• Concentrations on the numerator of $Q$ are those of the products;
• Concentrations on the denominator of $Q$ are those of the reactants.

As time proceeds,

• the concentration of the products will increase, while
• the concentration of the reactants will decrease.

In other words, the equilibrium will move towards the products.