Explanation​:
ΔG=−RT ln(K).
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​:
By applying Hess’s law, regardless of the route by which a chemical reaction proceeds, the enthalpy change will always have the same, provided that the initial and final states of the system are identical.

Explanation​:
Crude oil is non-renewable since there is a finite amount of this resource available on Earth. Crude oil has a high energy density meaning that it stores considerable energy in a smaller quantity than other energy sources.
Combusting crude oil releases sulfur and nitrogen oxides (thus contributing to acid precipitation) and carbon dioxide. Importantly, carbon dioxide is always a product of hydrocarbon combustion.

The question difficulty is categorized as a medium because there are a number of facts that the student must remember to answer this question correctly, but there is nothing that the student must solve to arrive at the correct answer.

Explanation:
The full, balanced equation divided into the balanced half-reactions where the hydrogen gas is oxidized, and the oxygen gas is reduced, is:

Anode half-reaction: 2H2(g) →4H^+(aq)+4 e^−

Cathode half-reaction: O2(g)+4H+(aq)+4e^− →2H2O(l)

The number of electrons required from these half-reactions can be identified as 4.

This question is categorized as hard. The student must be able to separate the hydrogen and oxygen gases to their correct electrodes and determine which is oxidized and which is reduced.
The easiest way to start this is to recognize that if the hydrogen were to be reduced, then it become negatively charged, which is not as stable as the cationic form (H+). Therefore, the hydrogen gas must be oxidized and the oxygen gas reduced.
From that point, the student must correctly place the water in the oxygen’s half-reaction.

Another strategy that is effective is to determine the oxidation state changes for the elements in each half-reaction. Oxidation will occur at the anode, and so the half-reaction must have an increased change in oxidation state. At the cathode, reduction will be occurring and so the oxidation state will decrease.

Explanation:
As temperature increases, the equilibrium shifts to the left hand side (more blue) to oppose the change.
The backward reaction is therefore endothermic and absorbs energy, whereas the forward reaction is exothermic.
As equilibrium shifts to the left, Kc​ decreases as the concentration of reactants increases.

Explanation​:
Gases have the highest entropy followed by liquids and then solids.
CO2​ has a higher entropy than O2 because it has more bonds, and therefore, more vibration modes.

Explanation​:
At equilibrium, Gibbs free energy is at a minimum.

Explanation:
Atomisation is defined as the formation of one mole of gaseous atoms.
Ionization is the process in which one mole of electrons is removed from one mole of gaseous atoms/ions.
Electron affinity is the addition of one mole of electrons to gaseous atoms/ions.

Explanation:
Many products can be made from the same reactants by more than one route. Regardless of the route by which a chemical reaction proceeds, the enthalpy change will always be the same provided that the initial and final states of the system are identical.

Explanation:
Coal is an impure form of fossil fuel and therefore contains many impurities that will also combust. This will result in many byproducts from the impurities combusting, so more oxygen is required to combust the hydrocarbons completely.
Propane, natural gas, and crude oil are all cleaner fuels (have fewer impurities). So, they are more likely to undergo complete combustion with a comparable amount of oxygen per mole of fuel.

Explanation​:
Endothermic reactions absorb energy from the surroundings. This decreases the temperature of the surroundings and increases the energy in the bonds (the system).

Explanation​:
The reaction is taking place under standard conditions, so it is fair to use standard enthalpies of formation to calculate $\Delta$Hr​. Even if the reaction takes place under non-standard conditions, the error is typically small unless a phase transition such as boiling or melting has taken place. In their standard states, carbon is a solid and bromine is a liquid, but it is not necessary for the elements to be gases as the enthalpy of vaporisation is accounted for in the measurement of ΔHfθ​.

Bond energy calculations do not account for the enthalpy changes of boiling, melting and sublimation, but the reactants and products in this reaction are gases so such errors are not relevant. The bond energies may, however, differ from the average values; for example, the C-H bond energies in the product may be affected by the neighbouring C-Br bond.

This question is only moderately difficult as the errors and assumptions of the two calculation methods are clearly stated in the syllabus.

Explanation:
In an electrochemical fuel cell, the fuel (methanol, for example) is oxidized at the anode, while oxygen gas is reduced at the cathode to form water. As is the case for any electrochemical cell, the electrons flow through an external wire from the anode to the cathode.

This question is categorized as medium because it requires the knowledge that oxygen gas is reduced at the cathode and that the product is water. The CO2​ would be a product for oxidizing a fuel such as methanol.

Explanation​:
When a metal is combusted, a tremendous amount of energy is released in the form of heat or light. Since the energy is released, the reaction is exothermic, and the enthalpy is negative.
Additionally, the product of the combustion of the metal is the synthesis of the metal oxide.

This question is a medium difficulty where the student must know that combustions are exothermic and correspond to a negative enthalpy change. Further, the student must recognize that in the product compound, magnesium oxide, the magnesium has a +2 charge, and the oxygen has a −2 charge, resulting in MgO.

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 $t$; therefore, the reactants must have more moles of gas than the products.

Explanation​:
The graph shows that the maximum change in temperature is 24.9−20.0=4.9°C. However, extrapolating the linear cooling trend to the time of addition gives a theoretical maximum change of 5.4$°$C. This is the value of $\Delta T$ that should be used to obtain the best estimate of $q$, as the extrapolation accounts for heat loss to the environment during the reaction.

The other distractors correspond to the temperature change at the latest recorded time point (option A) and the extrapolated temperature change at time = 0$s$ (option D), a time point which precedes the addition of the solid and is therefore irrelevant.

This question is moderately difficult as the student must interpret a graph and apply the heat loss correction with little guidance.

Explanation:
The formation of ethanol in biofuel occurs during the fermentation of plant material in anaerobic conditions and in the presence of yeast as a biological catalyst:

C6H12O6+yeast →2CH3CH2OH+2 CO2​

To eliminate the incorrect answers, students must recognize that carbon fixation is the process where inorganic carbon (such as CO2​) is converted to organic compounds during photosynthesis.
Combustion of hydrocarbons would be the process that would take place when the biofuel is combusted.

This question is categorized as easy since the student needs only to recall that ethanol for biofuel is produced via the fermentation of plant material.

Explanation:​
Average bond enthalpies give data for species in the gaseous phase. In choice C, water is a liquid and so the enthalpy change for the condensation of water vapour would also be needed.

Explanation:
Increased temperature increases the kinetic energy of the gas particles and therefore increases the disorder. Gases are more disordered than liquids and solids. The greater the pressure, the lower the disorder.

Explanation:​
The products are at a lower energy level than the reactants meaning that the total average bond enthalpy of formation of bonds in the products is greater than the total average bond enthalpy of breaking of bonds in the reactants.