Chemistry 2023 Jamb Examination

For a reversible exothermic reaction, heat can be considered a product. When the temperature decreases, the system shifts in the direction that produces more heat to counter the change according to Le Chatelier’s principle.
This means the equilibrium shifts to the right (towards the products) to release more heat and restore balance.

Radon (Rn) is a radioactive noble gas formed naturally from the decay of uranium and thorium in the Earth's crust.
It is colourless, odourless, and tasteless, but highly radioactive and can accumulate in enclosed spaces, posing health risks when inhaled over time.

Entropy measures the degree of disorder in a system. When a substance changes from a liquid to a gas, there is a large increase in the randomness and energy distribution of particles.
Therefore, the change from liquid to gas results in the highest increase in entropy compared to other phase changes listed.

In any neutral compound, the sum of all oxidation numbers of the atoms must equal zero because the total positive and negative charges balance each other.
For example, in water (H\(_2\)O), the oxidation number of hydrogen is +1 and oxygen is -2, giving a total of 2(+1) + (-2) = 0.

The kinetic theory of gases explains that gas particles are in constant random motion. The pressure exerted by a gas arises from the collisions of these particles with the walls of the container.
The more frequent and forceful the collisions, the higher the pressure. The theory assumes that the size of gas particles and intermolecular forces are negligible.

Eutrophication occurs when water bodies receive excess nutrients, especially nitrates and phosphates, often from agricultural runoff or sewage discharge.
This nutrient enrichment promotes the overgrowth of algae (algal bloom), which depletes oxygen levels in the water, leading to the death of aquatic organisms and ecological imbalance.

The Haber process is the industrial method used to synthesise ammonia (NH\(_3\)) from nitrogen (N\(_2\)) and hydrogen (H\(_2\)) gases under high temperature and pressure, in the presence of an iron catalyst.
This process revolutionised agriculture by enabling large-scale production of nitrogen-based fertilisers.

Niels Bohr proposed the planetary model of the atom, where electrons revolve around the nucleus in fixed energy levels or shells, much like planets orbit the sun.
This model explained atomic emission spectra, marking a major advancement from Rutherford’s earlier nuclear model of the atom.

Endothermic reactions absorb heat from their surroundings. During the decomposition of hydrogen peroxide (H\(_2\)O\(_2\)), energy is absorbed to break the chemical bonds, forming water and oxygen gas.
This contrasts with combustion and formation reactions, which are typically exothermic, releasing heat energy.

When a chemical reaction is reversed, the equilibrium constant for the new reaction becomes the reciprocal of the original Kc value.
This is because the concentrations of products and reactants in the expression for Kc are interchanged, effectively inverting the ratio.