Revision Chemistry Questions For University Freshers July 2020
CHEMISTRY (CHE 101)
1. Question on Chemical Kinetics:
If doubling the concentration of a reactant increases the rate of reaction four times, what is the order of reaction with respect to the reactant?
N/B; Order of reaction is the power or exponent to which the reactant is raised in a rate equation. It is determined experimentally, and not stiochiometrically (or from the stiochiometrical equation). For example:
(where x+y is the order of reaction)
N/B; Rate Law: the law states that the rate of reaction is directly proportional to reactant concentration with respect to the order of reaction; the mathematical expression of the rate law is known as rate equation. i.e
………………….. (1) rate law
………………….. (2) rate equation
from equa (2) ……..
the reaction is therefore a second order reaction since
2. Question on Chemical Equilibrium
Calculate the equilibrium concentration of NO2 in a solution prepared by dissolving of N2O4 in 400ml of chloroform. For the reaction in chloroform,
What will be the percentage decomposition of the original
3. Question on Electromagnetic Radiation
What is an electromagnetic radiation?
What is the wavelength (in nanometers) that corresponds to an electron transition from the level to the level in the hydrogen atom?
3a. Electromagnetic Radiation (EMR) is the propagation of energy in wave form, with periodic changes in magnetic and electric fields. The following are characteristics of EMR:
Velocity (speed of light [c])
Frequency (f or v)
4. Question on Gas Laws
State Graham’s law of diffusion of gases. Express the equation in terms of rate, density, molar mass and time.
A mixture of two gases, A and B, of equal masses is made to diffuse through a porous pot. If it takes 30secs for A to diffuse through the pot, how long will it take B?
Express the Van Der Waal’s equation for real gases.
Graham’s law of diffusion of gases states that the rate of diffusion or effusion of a gas is inversely proportional to the square root of its density at constant temperature and pressure.
The expression of the equation in terms of rate, density, molar mass and time follows as
Expression of the Van Der Waal’s equation is also known as the real gas equation
5. Question on Acids/ Bases/ pH & pOH Analysis/ Nuclear Reactions
Water is said to be amphoteric. Illustrate this with a suitable example and equation
What are the differences between nuclear reactions and other chemical reactions?
An amphoteric substance is one that has the ability to donate hydrogen ion (H+) or accept hydrogen ion (H+) in solution. E.g. water (H2O), ammonia (NH3) etc. They behave both like an acid and a base in solution.
Differences between chemical and nuclear reactions
Only the electronic structure of the atoms are affected
The nucleus of the atoms are affected
Does not result in formation of a new element
Results in conversion of one element to another
Are affected by factors that affect rate of chemical reactions such as temperature and pressure
Are not affected by factors that affect rate chemical reactions
Small amount of energy is released or absorbed by the reaction
Large amounts of energy is released or absorbed by the reaction
Isotopes of an element show identical behaviour
Isotopes of an element behave differently