Explanation:​
Adding water will reduce the concentration (dilution), and, therefore the frequency of effective collisions will decrease.

Explanation:
The rate expression can only be determined experimentally.

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 $ln(2)$ term appears because k1​ is double k2​, and the factor of 1000 appears in the denominator to convert J mol−1to kJ mol−1.
Option B is almost correct, but the temperature terms 1/298​ and 1/308​ would need to be swapped to give a positive value for the activation energy.
The question is in the “hard” or “very hard” category since students must be able to identify the correct terms in the question for use in the equation, rearrange the equation correctly, and also perform a unit conversion.

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

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 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:​
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​:
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​:
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​:
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:​
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.

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:​
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​:

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

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

Explanation​:
Using the Arrhenius equation k = Ae−Ea/RT, a linear relationship will be created by graphing ln k vs. 1/T​