IB Chemistry 5 — Questions and Answers
Question 1: Which of the following best describes an exothermic reaction?
- ΔH > 0 and energy is absorbed from surroundings
- ΔH < 0 and energy is released to surroundings (Correct answer)
- ΔH = 0 and no energy change occurs
- ΔH > 0 and temperature of the system decreases
Correct answer: ΔH < 0 and energy is released to surroundings
In an exothermic reaction, ΔH is negative because the system releases energy to the surroundings, causing the temperature to rise.
Question 2: In titration, what is the equivalence point?
- The point where the indicator changes color
- The point where moles of acid equal moles of base (Correct answer)
- The midpoint of the titration curve
- The point where pH = 7
Correct answer: The point where moles of acid equal moles of base
The equivalence point is where the moles of titrant added exactly neutralize the moles of the analyte, not necessarily at pH 7.
Question 3: Which of the following is the correct definition of molarity?
- Moles of solute per kilogram of solvent
- Moles of solute per liter of solution (Correct answer)
- Grams of solute per liter of solution
- Moles of solute per mole of solution
Correct answer: Moles of solute per liter of solution
Molarity (M) is defined as the number of moles of solute divided by the volume of solution in liters.
Question 4: What does the Hess's Law state?
- Enthalpy change depends on the pathway taken
- The total enthalpy change of a reaction is the same regardless of the route taken (Correct answer)
- Entropy always increases in a spontaneous reaction
- The enthalpy of a reaction equals its activation energy
Correct answer: The total enthalpy change of a reaction is the same regardless of the route taken
Hess's Law states that the total enthalpy change of a reaction is independent of the pathway, depending only on initial and final states.
Question 5: Which of the following represents a homogeneous mixture?
- Sand and water
- Oil and water
- Saltwater (Correct answer)
- Granite rock
Correct answer: Saltwater
Saltwater is a homogeneous mixture because the solute (salt) is uniformly distributed throughout the solvent (water) at the molecular level.
Question 6: What is the role of the salt bridge in an electrochemical cell?
- To allow electrons to flow between half-cells
- To maintain electrical neutrality by allowing ion flow between half-cells (Correct answer)
- To speed up the oxidation reaction
- To store electrical energy
Correct answer: To maintain electrical neutrality by allowing ion flow between half-cells
The salt bridge allows ions to migrate between the two half-cells, maintaining electrical neutrality and completing the circuit.
Question 7: Which of the following is a property of transition metals that distinguishes them from main group metals?
- They are all diamagnetic
- They have fixed oxidation states only
- They can form colored compounds and exhibit variable oxidation states (Correct answer)
- They do not form complex ions
Correct answer: They can form colored compounds and exhibit variable oxidation states
Transition metals are characterized by their ability to form colored compounds and display variable oxidation states due to their partially filled d orbitals.
IB Chemistry 5
Which of the following best describes an exothermic reaction?