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​:
ΔG=ΔH−TΔS.
Negative $\Delta \mathrm{G}$ values result in spontaneous reactions.
Negative $\Delta \mathrm{H}$ and positive $\Delta \mathrm{S}$ values result in a negative $\Delta \mathrm{G}$ value at all temperatures.

C6H12O6+yeast →2CH3CH2OH+2CO2​

To eliminate the incorrect answers, students must recognize that carbon fixation is the process where inorganic carbon (such as CO2COX2​) 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:
To answer this question, the student must first recognize that oxygen gas is reduced at the cathode, and the fuel (methanol) is oxidized at the anode.
Next, it is essential to select the answer choice where the amount of electrons produced in the oxidation is equivalent to the electrons used in the reduction.
Finally, the question states the reaction is under acidic conditions, and therefore, the correct answer is the one that includes H+ as opposed to OH−.

This question is categorized as hard because there are many parameters to consider in order to select the correct answer:

• Cathode = site of reduction
• Anode = site of oxidation
• Electrons must be equal in each half-reaction
• Acidic conditions require H+ to be present in half-reactions

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:
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:
Born-Haber cycles are used for ionic compounds only.

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​:
Combining the first equation and the reverse of the second equation gives the equation for the enthalpy change in question. (+33.9 kJ)−(−56.5 kJ)=+90.4 kJ

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:​
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.

Explanation:
If a chemical reaction leads to an increase in enthalpy, the heat energy is absorbed from the surroundings.

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 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 standard enthalpy of formation of a pure element in its standard state is zero; not for a compound.

Explanation:​
Condensation (gas to liquid) requires making bonds and therefore, releases energy. Sublimation (solid to gas) requires breaking bonds and therefore absorbs energy.

Explanation​:
$\mathrm{G}$ becomes more negative as a spontaneous reaction proceeds until it reaches its minimum. At this point, there will be no net change, and the system has reached equilibrium. $\Delta \mathrm{G}$ will equal zero but $\mathrm{G}$ will not.

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

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 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:​
Four $C-H$ bonds and two $O=O$ bonds are broken. Two $C=O$ and four $O-H$ bonds are formed.
ΔH =$\Sigma$ΔHBEθ​(bonds broken) - ΣΔHBEθ(bonds formed).