Therefore, 0.5 moles of H2require 0.167 moles of N2 to completely react. There are $s$ of N2NX2​ available so N2 is the reactant in excess.

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:
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.

Explanation:
The balanced chemical equation is 2C3H7OH(l)+9 O2(g)→6 CO2(g)+8 H2O(l). The sum of the coefficients is $25$.

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:
Using trials 1 and 2, as [X] doubles, rate also doubles therefore first order with respect to [X].
Using trials 2 and 3, as [Y] halves, rate stays the same and so, zero order with respect to [Y].
This gives a slow step that depends on unimolecular X, and not Y.

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 rate constant, $k$, is the feature of the rate equation that is affected by temperature according to the Arrhenius equation k=Ae−Ea/RT.
The graph of rate vs temperature always shows this general trend, and similar questions have been asked several times in past papers.
The question is of moderate difficulty as the use of a specific example and reference to rate rather than k may derail some students. Confusion with the Arrhenius plot could also lead students to select option B.

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:​
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 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:​

The correct balanced equation is:

2LiOH + H2​SO4​ → Li2​SO4​ + 2H2​O.

2+1+1+2 = 6

Explanation​:
Increasing the volume decreases the pressure which shifts the position of the equilibrium to the right where there are more moles of gas.
The forward reaction is endothermic and so increasing the temperature favors this reaction.
A catalyst affects both the rate of the forward and reverse reactions equally and has no effect on the equilibrium yield.

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 molecularity is given by the power to which the species is raised to in the rate expression. X is raised to the power of two meaning the rate determining step involves two X molecules.

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:​
D has the steepest gradient when a tangent is drawn.

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​:
$)$.
If $\Delta G$ is positive, ln(K) must be negative. ln(K) is negative for values smaller than 1.
A positive $\Delta G$ value indicates that the reaction is not spontaneous. Therefore, the equilibrium concentrations of the reactants are larger than the ones of the products; the equilibrium constant is less than 1.

Explanation:​
All graphs are [A] vs time.
A linear plot of [A] vs time represents a zero order reaction, B and D represent first order reactions (B represents [A] as a product and is therefore increasing).
C is a second order plot of [A] vs time and has a steeper initial rate (slope) when compared to first order reactions.