Explanation:​
Students should be aware of the definition of frequency factor. However, questions on this topic are somewhat uncommon, and students could confuse this concept with the idea that molecules capable of successful collision lie above Ea​ in a Boltzmann distribution (leading them to select option D). The difficulty level is therefore at the higher end of the “easy” range.

Explanation​:
The coefficients of all species in the equation are halved which results in Kc​ being square rooted.
Kc​ = [NOCl2]2/[NO]2[Cl2]​

Explanation:​
Four factors that can increase the rate of a chemical reaction are: increasing the temperature of the reaction, adding a catalyst, increasing the concentration of the reactants and decreasing the solid particle size of the reactants.

Explanation​:
The equilibrium shifts to favor the endothermic reaction (forward) when the temperature is increased to resist that change (Le Chatelier’s principle).
Temperature is the only factor that changes the value of the equilibrium constant.

Explanation​:
OH− ions react with the H+ ions, thus decreasing their concentration. The equilibrium shifts towards the reactants to produce more H+ and resist this change (Le Chatelier’s principle). This produces more yellow chromate ions.
The value of Kc is only affected by temperature so this is unchanged.

Explanation​:
A dynamic equilibrium is reached in a closed system when the rates of the forward and reverse reactions are equal. The concentrations of reactants and products do not change but are non-stop being interconverted. The equilibrium could favor one side over the other.

Explanation​:

The theoretical yield is the maximum amount of product that will be formed if the limiting reagent is consumed completely.

Explanation​:
A catalyst provides an alternative pathway for the reaction lowering the activation energy. It affects both the forward and reverse reaction rates equally. The position of equilibrium will not change.

Explanation​:

Kc​ is written as the concentrations of the products divided by the concentrations of the reactants each raised to the power of the coefficient in the balanced equation.

Explanation​:
Graph D shows that rate is proportional to [A]2.
A and B are concentration-time graphs. C is a first order rate-concentration graph as they are directly proportional

Explanation​:
The ratio of SO3:SO2:O2 is 2:2:1. Therefore, half the number of moles of oxygen would be produced compared to SO2​

Explanation:​
Kc>1, and so lies towards the right with the yellow product at equilibrium; the color would therefore be a pale green due to more yellow than blue.
When an acid is added, it reacts with the OH− reducing its concentration. Equilibrium shifts to the right to oppose that change.

Kc only changes with temperature. Adding an alkali would increase the OH− concentration and therefore the equilibrium would shift to the left to oppose that change. Kc​ again would remain the same as it is only affected by temperature.

Explanation:
Using trials 1 and 2, as the concentration of I^− doubles, the rate also doubles. Rate and [I−] are therefore, directly proportional with an order of 1.

Explanation​:
The solid KI will dissolve until the solution is saturated and then a dynamic equilibrium will be established where the rate of precipitation is equal to the rate of dissolution of the excess solid.
The system must be closed and therefore no matter can be exchanged with the surroundings.

Explanation​:
The peaks represent transition states where energy is at its highest. This graph shows a multi-step mechanism where Y is an intermediate species between R and P. Catalysts lower the activation energy which is the difference between R and X.

Explanation:​
The rate constant increases with increasing A and decreases with increasing Ea​.
This question is on the lower end of the medium-difficulty category as students should be familiar with the effect of these variables on $k$, and are given the equation for assistance if needed.

Explanation:​
The y-intercept = $lnA$ so must be larger for reaction 1.
The gradient (slope) is equal to −Ea/R​​ so, must be shallower (less negative) for reaction 1.
The question is in the “hard” category as students must know how to interpret an Arrhenius plot (or correctly interpret the given equation) and compare two reactions graphically.

Explanation​:
Units for $k$ are determined by dividing the units of rate by the units of the concentrations raised to their respective powers.
For a 3rd order reaction, k=mol dm−3 s−1/mol3 dm−9 = mol−2 dm6 s−1.

Explanation​:
Q>Kc, therefore the backward reaction will be favored as the system approaches dynamic equilibrium.
The backward reaction is endothermic, so the temperature will decrease.
There are more moles of gas on the left and so pressure increases. NO2​ is red-brown and so the gas mixture will get darker.

Explanation:
The endothermic reaction is favoured when the temperature increases. The concentration of products increases at t=10 mins; therefore, the forward reaction must be endothermic.
Increasing the volume decreases the pressure and causes the side with more moles of gas to be favoured. The concentration of reactants increases at t=15 mins; therefore, the reactants must have more moles of gas than the products.