CPT Chemical Process Fundamentals & Reactions 1 — Questions and Answers
Question 1: What does Le Chatelier's Principle state about a chemical system at equilibrium?
- The system will shift to counteract any stress applied to it (Correct answer)
- The reaction rate always increases when temperature drops
- Catalysts change the position of equilibrium
- Pressure has no effect on gas-phase reactions
Correct answer: The system will shift to counteract any stress applied to it
Le Chatelier's Principle states that if a stress (temperature, pressure, concentration change) is applied to an equilibrium system, it will shift to partially oppose that stress.
Question 2: Which of the following best describes an exothermic chemical reaction?
- A reaction that absorbs heat from the surroundings
- A reaction that releases heat into the surroundings (Correct answer)
- A reaction that occurs only at low temperatures
- A reaction that requires a catalyst to proceed
Correct answer: A reaction that releases heat into the surroundings
An exothermic reaction releases energy (heat) into the surroundings, resulting in a negative enthalpy change (ΔH < 0).
Question 3: What is the primary role of a catalyst in a chemical reaction?
- It is consumed during the reaction to produce more product
- It increases the equilibrium yield of the products
- It lowers the activation energy without being consumed (Correct answer)
- It raises the temperature required to initiate the reaction
Correct answer: It lowers the activation energy without being consumed
A catalyst lowers the activation energy of a reaction, speeding it up without being consumed or altering the equilibrium position.
Question 4: In a process plant, pH is a measure of which property of an aqueous solution?
- Concentration of dissolved solids
- Hydrogen ion (H⁺) activity or acidity/basicity (Correct answer)
- Oxidation-reduction potential
- Total dissolved oxygen content
Correct answer: Hydrogen ion (H⁺) activity or acidity/basicity
pH measures the hydrogen ion (H⁺) activity in solution; values below 7 are acidic, above 7 are basic, and 7 is neutral.
Question 5: Which statement correctly distinguishes a physical change from a chemical change?
- Physical changes always produce new substances with different chemical formulas
- Chemical changes are always reversible under normal conditions
- Physical changes alter form or state without producing new substances (Correct answer)
- Chemical changes do not involve any energy transfer
Correct answer: Physical changes alter form or state without producing new substances
A physical change alters the form, size, or state of matter without creating new chemical substances, while a chemical change produces new substances.
Question 6: What unit is most commonly used to express the rate of a chemical reaction in a process setting?
- Moles per liter per second (mol/L·s) (Correct answer)
- Kilograms per cubic meter (kg/m³)
- Joules per mole (J/mol)
- Pascals per kelvin (Pa/K)
Correct answer: Moles per liter per second (mol/L·s)
Reaction rate is expressed as the change in concentration (moles per liter) per unit time (per second), giving mol/L·s.
Question 7: When temperature increases in a reversible exothermic reaction, what shift in equilibrium is expected?
- Equilibrium shifts toward the products
- Equilibrium shifts toward the reactants (Correct answer)
- Equilibrium remains unchanged
- Activation energy decreases and yield increases
Correct answer: Equilibrium shifts toward the reactants
According to Le Chatelier's Principle, adding heat to an exothermic reaction shifts the equilibrium toward the reactants to absorb the excess energy.
CPT Chemical Process Fundamentals & Reactions 1
What does Le Chatelier's Principle state about a chemical system at equilibrium?