VCAA Chemistry How can the rate and yield of chemical reactions be optimised?

The capacity (extent of reaction) of a lithium-ion cell actually decreases over time with repeated recharging due to the gradual degradation of the electrodes.

Battery voltage is determined by the potential difference between the cell components (thermodynamics), not the rate of the chemical reaction (kinetics).

As a battery discharges and the extent of the forward reaction increases, the battery voltage typically decreases rather than increases.

Temperature is proportional to the average kinetic energy of the particles, which determines the spread and peak position of the curve, not the total area.

The Maxwell-Boltzmann distribution describes the kinetic energy or speed of particles, not their chemical potential energy.

While collision frequency is related to particle speed, the area under the curve specifically represents the total number of particles, not how often they collide.

This is incorrect because the stoichiometric coefficient of the reactant (2) must be used as an exponent, not a multiplier. The correct term is $[\text{HI}]^2$, not $2[\text{HI}]$.

This is incorrect because it uses atomic species (H, I) instead of the molecular species ($\text{H}_2$, $\text{I}_2$) actually present in the reaction, and it treats coefficients as multipliers rather than exponents.

This is incorrect because it substitutes atomic concentrations for molecular products and uses coefficients as multipliers in the numerator.

Side reactions do occur in secondary cells, which is why they gradually degrade over time and have a limited number of recharge cycles.

Fuel cells are not secondary cells; they require a continuous supply of external reactants (fuel and oxidant) to generate electricity, whereas secondary cells store chemical energy internally.

The polarity of the cathode changes depending on the cell's operation: it is positive during discharge (galvanic cell) but negative during recharge (electrolytic cell).

A catalyst does not change the speed of the particles. Increasing the temperature of the system would increase particle speed.

A catalyst does not increase the frequency of collisions. Factors like increased concentration, pressure, or temperature would increase the number of collisions per unit time.

The overall kinetic energy of the system is determined by its temperature, not by the presence of a catalyst.

This value is $(K_c)^2$, which would be the equilibrium constant if the first reaction were multiplied by 2 but not reversed.

This value is $2 \times K_c$. When a reaction is multiplied by a coefficient, the equilibrium constant must be raised to that power, not multiplied by it.

This value results from incorrect mathematical manipulation of the equilibrium constant. The correct operation is to take the inverse square of the original $K_c$.

This is incorrect because natural photosynthesis produces glucose and oxygen, whereas artificial photosynthesis typically produces hydrogen gas or other synthetic fuels.

This is incorrect because the reduction of hydrogen ions ($H^+$) to hydrogen gas ($H_2$) occurs at the cathode, not the anode.

This is incorrect because artificial photosynthesis relies on solar energy (light) to drive the oxidation of water, rather than electrical energy from an external power supply.

While catalysts do lower the activation energy required, they function to speed up the reaction, not slow it down.

Catalysts lower the activation energy required for the reaction to occur, rather than requiring more energy.

This is incorrect because catalysts lower the activation energy and increase the rate of reaction.

While increasing the partial pressure of a reactant does increase the yield, it also increases (rather than decreases) the reaction rate due to a higher frequency of molecular collisions.

Increasing temperature increases the kinetic energy of the molecules, which always leads to an increase in the reaction rate, not a decrease.

The reaction forming $NO_2$ is exothermic; therefore, increasing the temperature shifts the equilibrium toward the reactants (left), decreasing the yield of $NO_2$.

System X has a higher initial concentration of $\text{CH}_4\text{(g)}$ (2 M vs 1 M), which results in a higher initial rate of the forward reaction compared to system Y.

Because system X produces a higher concentration of products at equilibrium, the rate of the backward reaction (which depends on product concentrations) will be higher in system X than in system Y.

While 3 moles of $\text{H}_2\text{(g)}$ are produced for every mole of $\text{H}_2\text{O(g)}$ consumed, this stoichiometric ratio applies to the change in amounts, not their final equilibrium concentrations.

If the rate of evaporation were less than the rate of condensation, the amount of liquid water would increase, causing the water level to rise.

If the rate of evaporation were greater than the rate of condensation, the amount of liquid water would decrease, causing the water level to drop.

While the rates are equal, they are not zero because molecules are constantly escaping and returning to the liquid surface in a state of dynamic equilibrium.

While the anode is negative in a galvanic cell, it is positive in an electrolytic cell because it is connected to the positive terminal of the power supply.

Half-cells must be separated in a galvanic cell to prevent direct reaction, but they can often be placed in the same container in an electrolytic cell.

Galvanic cell reactions are spontaneous and exothermic, but electrolytic cell reactions are non-spontaneous and endothermic, requiring an input of electrical energy.