Equilibrium Reactions Trivia Quiz

Answer: After attaining equilibrium, the reaction ceases

Equilibrium reactions are dynamic. No change may seem to be happening, but that is just because the reverse reaction rate is equal to the forward reaction rate - keeping the amounts of the concerned substances balanced.

Another common misconception about equilibrium reactions is that, after attaining equilibrium, the concentration of reactants and products are equal and stay equal. This is a possibility, but not a necessity. The respective concentrations may be unequal (as they mostly are), but they just don't change.

Answer: Both reactions are favored equally

The role of a catalyst is to provide an alternate pathway which requires a lower activation energy, and this is true for both the reverse and forward reactions.

Both reactions being favored equally means that equilibrium is reached more quickly, but the equilibrium concentrations of the reactants or products stays the same; i.e. the position of equilibrium stays the same.

Answer: 50

It is necessary to write down the balanced equation of the reaction first.

CO + 2H2 ⇌ CH3OH

Thus the equilibrium expression would be: (Concentration of Methanol)/(Concentration of Carbon Monoxide) * (Concentration of Hydrogen)^2

You will get the correct answer after plugging in the values.

Although the units are mostly not needed for Kc, it would be moles^-2 dm^6.

Answer: x/y

Suppose your reaction is:-

aX + bY ⇌ cZ + dW, where X,Y,Z and W are the reactants and products while a, b, c and d are respectively the stoichiometric coefficients in the formula of the reaction.

The rate of forward reaction = x *[Z]^c * [W]^d and the rate of backward reaction = y * [X]^a * [Y]^b

Since the rate of forward reaction is equal to that of the backward reaction ->
(x *[Z]^c * [W]^d )= (y * [X]^a * [Y]^b)

Transposing the equilibrium expression on one side would be equal to x/y.

Answer: Kp = Kc/90000R^2

The general term for the relation between the two is:-

Kc = Kp (RT)^Δn , where R is the universal gas constant, T is the temperature, Δn is the change in gaseous moles.

In order to know the latter, you may have to write the equation down:-
N2 + 3H2 ⇌ 2NH3

There are four gaseous moles on the reactants' side, two on the products'.
Hence, Δn = -2.

Plug the values into the formula, without forgetting to change the unit of temperature to Kelvin, which will be 300 K.

Although R is a constant with a fixed value, I didn't enter its value in the answer because the units used may have to be clarified upon (lazy me!), and so that it is easier to do your calculations manually.

Answer: x^(-1/4)

Often, diatomic gases are written with 1/2 as their stoichiometric coefficients. Since all the coefficients are being divided by 4, the entire equilibrium expression will have its powers divided by 4.

Notice that we are concerned with the reverse reaction of our original reaction. The equilibrium constant of the forward reaction is the inverse of the equilibrium constant for the backward reaction.

Answer: K1 * K2

Temperature is not needed when the equilibrium constants are already given.

K1 = Concentration of water / Concentration of water vapor

K2 = Product of the concentrations of the ions / Concentration of water

If you multiply them, through cancellation you get {K1 * K2 =} product of the concentrations of the ions / Concentration of water vapor, which will be the equilibrium constant for the overall reaction.

Answer: The shape changes, but the mass remains the same

Remember that this is dynamic equilibrium. The reactants and products continue to react, although they completely negate each other. This means that the rate of melting is equal to the rate of freezing of the sugar molecules, so the mass doesn't change. But since melting still continues, the shape of the cube will be worn down.

Answer: Gas fizzes out, equilibrium shifts to the side with dissolved air

This is an example of equilibrium in physical processes. The equilibrium can be represented as:-

CO2 (aq) ⇌ CO2 (g)

When the seal is opened, the pressure has decreased. In order to make up for the lost pressure, the equilibrium responds by producing more gaseous molecules. Hence, the equilibrium shifts to the right and further carbon dioxide is released.

Answer: Remove some of the chlorine from the reaction

Adding a catalyst, as has been mentioned in the quiz, has no effect whatsoever on the position of equilibrium as both the forward and backward reactions are boosted equally.

When the pressure is increased, the equilibrium shifts to reduce the pressure - which is to the left, since the reactants' side has only one gaseous molecule compared to two in the products' side.

When the volume of the system is decreased, the respective concentrations of the substances increase. Since there are more molecules on the products' side, the value of Kc would increase were it not for the Le Chatelier principle. In order to resist any change in the value of Kc, the reverse reaction increases and equilibrium shifts to the left.

If chlorine is removed from the reaction, the forward reaction increases to replenish the lost chlorine and equilibrium shifts to the right.

Answer: False

The expression for the equilibrium constant is (Reaction's products powered to their stoichiometric coefficients multiplied)/ (Reaction's reactants powered to their stoichiometric coefficients multiplied with each other).

If the value of the constant is below 1, quite clearly the denominator is greater and the reactants are favored to some extent. If the value is below 10^-2, the reactants are considered to be dominant in the equilibrium mixture and the reaction has hardly proceeded. If the value is above 10^2, the products are dominant and little reverse reaction has taken place. Anything between these values means that both are present in noticeable amounts.

Answer: 5/16

Did you fall for the trick? Adding or removing reactants/products has no results on the value of Kc or Kp - it is after all the CONSTANT of equilibrium. The position of equilibrium is shifting precisely to minimise the effect of the change on Kc, as has been noted by the Le Chatelier principle. Don't be distracted by the information about 1 mole of each constituent being removed.

Remember that the amounts are not equal to the concentration. The concentrations of A, B and C in a 10L container would respectively be 0.4, 0.4 and 0.5 molars respectively.

The concentration of the product of the reaction divided by the the concentrations of the reactants multiplied would give you the correct answer.

Answer: The reaction rate may be too slow

The Contact Process is an important step in the production of sulphuric acid, a substance with manifold applications. Remember that the Kc of a reaction only tells you the position of an equilibrium reaction, not how quickly you are going to attain it.

As we may have learnt in chemical kinetics, the lower the temperature, the lower the rate of reaction. Although the concentration of sulfur trioxide will be higher, the slower rate of reaction is unfeasible for industrial mass production.

Answer: The equilibrium point respresents the lowest value of Gibbs Free energy

The relation between Gibbs free energy and the equilibrium constant is given by the van' t Hoff Isotherm :-

ΔG = -RT * natural log of Kc

When the ΔG for a reaction is negative, the ΔG for the reverse reaction would be positive. This may seem to imply that only the forward reaction is spontaneous, and hence proceeds to completion. However, the equilibrium point represents an intermediate stage with the lowest Gibbs free energy. This means that both the reactions remain spontaneous, as should be for an equilibrium reaction.

Answer: Just decrease temperature

Since there are two gaseous molecules on both sides of the equilibrium, there is no change in the position of equilibrium when the pressure of the system is altered. If the enthalpy is positive, the reaction is endothermic. The equilibrium reacts to the change by producing more heat, according to the Le Chatalier principle. This is done by increasing the rate of backward reaction.

Nitrogen monoxide is a highly toxic gas produced from the exhaust fumes of a vehicle, which is responsible for both the greenhouse effect and acid rain; which is why automobile manufacturers try to set up conditions which reduce their yield.