Chemical Systems Practice Questions
Matric (South Africa) · Matric Physical Sciences · 146 free MCQs with instant results and detailed explanations.
146
Total
43
Easy
75
Medium
28
Hard
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Sample Questions from Chemical Systems
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Q1
Easy
Which of the following best defines a chemical system?
A.
A chemical system includes only the reactants in a reaction.
B.
A chemical system consists of the reactants, products, and the environment.
C.
A chemical system is solely the products formed in a reaction.
D.
A chemical system refers only to the energy changes during a reaction.
Show Answer & Explanation
Correct Answer: B
A chemical system encompasses all components involved in a chemical reaction, including reactants, products, and their surroundings, which interact with each other.
Q2
Easy
In a closed container, if a gas is compressed to half its volume while keeping the temperature constant, what happens to the pressure of the gas?
A.
The pressure remains the same.
B.
The pressure decreases.
C.
The pressure doubles.
D.
The pressure triples.
Show Answer & Explanation
Correct Answer: C
According to Boyle's Law, when the volume of a gas decreases at constant temperature, the pressure increases proportionately. Halving the volume results in doubling the pressure.
Q3
Easy
What is the primary factor that affects the rate of a chemical reaction?
A.
The volume of the reaction vessel.
B.
The concentration of the reactants.
C.
The color of the reactants.
D.
The shape of the reaction container.
Show Answer & Explanation
Correct Answer: B
The concentration of reactants directly influences the rate of a chemical reaction; higher concentrations lead to more frequent collisions between reactant particles, increasing the reaction rate.
Q4
Medium
Which of the following describes the process of a solution reaching equilibrium?
A.
The rate of solute dissolving equals the rate of solute crystallizing.
B.
The temperature of the solution stops changing.
C.
All solute has dissolved into the solvent.
D.
The pressure remains constant in the solution.
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Correct Answer: A
At equilibrium, the rate of dissolving solute is equal to the rate of crystallization, resulting in no net change in concentration of solute in solution.
Q5
Medium
In a reaction where 2 moles of A react with 3 moles of B to produce C, how many moles of B are needed if 4 moles of A are used?
A.
6 moles
B.
5 moles
C.
4 moles
D.
3 moles
Show Answer & Explanation
Correct Answer: A
From the stoichiometry of the reaction, the ratio of A to B is 2:3. Therefore, for 4 moles of A, you need (4 moles A * 3 moles B / 2 moles A) = 6 moles of B.
Q6
Medium
What effect does increasing temperature have on the solubility of most solids in liquids?
A.
Increases solubility.
B.
Decreases solubility.
C.
No effect on solubility.
D.
Causes total insolubility.
Show Answer & Explanation
Correct Answer: A
For most solid solutes, increasing the temperature enhances the solubility in liquids due to increased kinetic energy, which allows more solute particles to interact with solvent molecules.
Q7
Medium
Which statement is true regarding exothermic reactions?
A.
They absorb energy from the surroundings.
B.
They release energy to the surroundings.
C.
They require constant heat input.
D.
They do not change the temperature of the surroundings.
Show Answer & Explanation
Correct Answer: B
Exothermic reactions release energy into their surroundings, typically in the form of heat, which is why the temperature of the surroundings may increase.
Q8
Hard
In a closed system, a reaction at equilibrium has the following equilibrium constant expression: Kc = [C]^c / [A]^a[B]^b. If the concentrations of A, B, and C are doubled, how does the equilibrium constant change?
A.
It remains unchanged.
B.
It doubles.
C.
It quadruples.
D.
It becomes half.
Show Answer & Explanation
Correct Answer: A
The equilibrium constant Kc is dependent only on the temperature and not on the concentrations of the reactants or products. Therefore, even if the concentrations are doubled, Kc remains unchanged.
Q9
Hard
A chemical reaction has an activation energy of 75 kJ/mol. If the temperature is increased from 300 K to 350 K, what effect does this have on the rate constant (k) according to the Arrhenius equation?
A.
k decreases significantly.
B.
k remains constant.
C.
k increases exponentially.
D.
k increases linearly.
Show Answer & Explanation
Correct Answer: C
According to the Arrhenius equation, an increase in temperature increases the kinetic energy of the molecules, leading to more effective collisions and thus an exponential increase in the rate constant k.
Q10
Hard
In a closed vessel, 2 moles of nitrogen gas (N₂) and 3 moles of hydrogen gas (H₂) are allowed to react to form ammonia (NH₃) according to the equation N₂(g) + 3H₂(g) ⇌ 2NH₃(g). What will be the total pressure in the vessel if the reaction reaches equilibrium at a temperature of 300 K, assuming ideal gas behavior and a volume of 10 L?
A.
5.28 atm
B.
2.64 atm
C.
4.12 atm
D.
3.92 atm
Show Answer & Explanation
Correct Answer: A
The reaction produces 2 moles of NH₃ from 1 mole of N₂ and 3 moles of H₂, reducing the total number of moles in the reaction. At equilibrium, the moles of NH₃ formed will be 2. Using the ideal gas law (PV = nRT), we calculate the total pressure based on the number of moles present.
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Chemical Systems — Matric (South Africa) Matric Physical Sciences Practice Questions Online
This page contains 146 practice MCQs for the chapter Chemical Systems in Matric (South Africa) Matric Physical Sciences. The questions are organized by difficulty — 43 easy, 75 medium, 28 hard — so you can choose the right level for your preparation.
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