Physical Chemistry

Question 1

What is the unit of the rate constant for a first-order reaction?

Accepted Answer

s⁻¹

Answer

For a first-order reaction, the rate law is expressed as Rate = k[A], where Rate has units of concentration per time (e.g., mol L⁻¹ s⁻¹) and [A] has units of concentration (e.g., mol L⁻¹). To make the units consistent, the rate constant (k) must have units of inverse time. Therefore, the unit for the rate constant of a first-order reaction is s⁻¹ (or min⁻¹, hr⁻¹, etc.).

Question 2

Which law relates the pressure, volume, and temperature of an ideal gas?

Accepted Answer

Ideal gas law

Answer

The Ideal Gas Law is a fundamental equation that describes the behavior of an ideal gas. It relates the pressure (P), volume (V), number of moles (n), and absolute temperature (T) of a gas through the equation PV=nRT, where R is the ideal gas constant. This law combines and extends Boyle's, Charles's, and Avogadro's laws into a single comprehensive relationship.

Question 3

What is the enthalpy change for a reaction at constant pressure called?

Accepted Answer

Enthalpy change

Answer

The enthalpy change (ΔH) for a reaction represents the heat absorbed or released during a chemical process carried out at constant pressure. It is a state function and is a key thermodynamic quantity used to describe the energy changes in chemical reactions. If ΔH is negative, the reaction is exothermic; if positive, it is endothermic.

Question 4

What is the term for the measure of disorder in a system?

Accepted Answer

Entropy

Answer

Entropy (S) is a thermodynamic property that quantifies the degree of randomness or disorder within a system. A system with higher entropy has more possible microstates for its particles, indicating greater disorder. The second law of thermodynamics states that the total entropy of an isolated system can only increase over time, or remain constant in ideal cases.

Question 5

Which of the following processes is exothermic?

Accepted Answer

Condensation

Answer

An exothermic process is one that releases energy, typically in the form of heat, to its surroundings. Condensation is the phase transition where a gas changes into a liquid. During this process, the molecules lose kinetic energy and form intermolecular bonds, releasing the latent heat of vaporization into the surroundings, thus making it an exothermic process.

Chemistry Practice Test Practice Test

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Physical Chemistry