PCAT Chemistry 5 — Questions and Answers
Question 1: Which of the following statements about catalysts is correct?
- A catalyst increases the activation energy of a reaction
- A catalyst is consumed during the reaction
- A catalyst lowers the activation energy without being consumed (Correct answer)
- A catalyst changes the equilibrium constant of a reaction
Correct answer: A catalyst lowers the activation energy without being consumed
A catalyst provides an alternative reaction pathway with a lower activation energy and is regenerated at the end, so it is not consumed.
Question 2: According to Le Chatelier's Principle, if the temperature of an exothermic reaction at equilibrium is increased, the equilibrium will shift:
- Toward the products
- Toward the reactants (Correct answer)
- Remain unchanged
- Depend only on concentration changes
Correct answer: Toward the reactants
For an exothermic reaction, heat can be considered a product; adding heat (raising temperature) shifts the equilibrium toward the reactants to absorb the excess heat.
Question 3: The electron configuration of Fe2+ (iron II ion, atomic number 26) is:
- [Ar] 3d6 4s2
- [Ar] 3d6 (Correct answer)
- [Ar] 3d4
- [Ar] 3d5 4s1
Correct answer: [Ar] 3d6
Fe has [Ar] 3d6 4s2; when Fe2+ forms, the two 4s electrons are removed first, giving [Ar] 3d6.
Question 4: Which of the following is true about a reaction with a large positive equilibrium constant (K >> 1)?
- The reaction strongly favors reactants at equilibrium
- The reaction strongly favors products at equilibrium (Correct answer)
- The reaction proceeds very quickly
- The reverse reaction is spontaneous
Correct answer: The reaction strongly favors products at equilibrium
A large K value (K >> 1) indicates that at equilibrium the concentration of products greatly exceeds the concentration of reactants.
Question 5: What is the oxidation state of manganese (Mn) in KMnO4?
- +2
- +4
- +6
- +7 (Correct answer)
Correct answer: +7
In KMnO4, K is +1 and each O is -2 (total -8); to balance, Mn must be +7: (+1) + Mn + (-8) = 0.
Question 6: Which type of isomerism involves compounds that have the same molecular formula and same connectivity but differ in the spatial arrangement of atoms?
- Constitutional isomerism
- Stereoisomerism (Correct answer)
- Functional group isomerism
- Chain isomerism
Correct answer: Stereoisomerism
Stereoisomers have the same molecular formula and connectivity (bonding sequence) but differ in the three-dimensional arrangement of their atoms in space.
Question 7: Which of the following best describes the colligative property of boiling point elevation?
- It depends on the identity of the solute particles
- It depends only on the number of solute particles in solution (Correct answer)
- It is greater for ionic solutes that do not dissociate
- It decreases as solute concentration increases
Correct answer: It depends only on the number of solute particles in solution
Boiling point elevation is a colligative property, meaning it depends on the number (not the identity) of dissolved solute particles per kilogram of solvent.
PCAT Chemistry 5
Which of the following statements about catalysts is correct?