Tahsili Chemistry 2 — Questions and Answers
Question 1: What is Le Chatelier's Principle?
- Chemical reactions always go to completion
- If a system at equilibrium is disturbed, it shifts to counteract the change and restore equilibrium (Correct answer)
- All reactions are reversible
- Temperature has no effect on equilibrium
Correct answer: If a system at equilibrium is disturbed, it shifts to counteract the change and restore equilibrium
Le Chatelier's Principle states that when a system at equilibrium is subjected to a change (concentration, temperature, pressure), the system adjusts to partially counteract the change. For example, adding reactant shifts equilibrium toward products.
Question 2: What is the difference between an exothermic and endothermic reaction?
- There is no difference
- Exothermic releases heat to surroundings (ΔH < 0); endothermic absorbs heat from surroundings (ΔH > 0) (Correct answer)
- Exothermic is slow; endothermic is fast
- Exothermic needs a catalyst; endothermic doesn't
Correct answer: Exothermic releases heat to surroundings (ΔH < 0); endothermic absorbs heat from surroundings (ΔH > 0)
Exothermic reactions release energy as heat (products have lower energy, ΔH negative): e.g., combustion. Endothermic reactions absorb energy (products have higher energy, ΔH positive): e.g., photosynthesis, dissolving ammonium nitrate.
Question 3: In a galvanic cell, what happens at the anode?
- Reduction occurs
- Oxidation occurs — the anode loses electrons (Correct answer)
- No reaction occurs
- Ions are deposited
Correct answer: Oxidation occurs — the anode loses electrons
At the anode, oxidation occurs (loss of electrons). Remember: AN OX, RED CAT — ANode = OXidation, REDuction = CAThode. The anode is the negative electrode in a galvanic cell. Electrons flow from anode to cathode through the external circuit.
Question 4: What is the molecular geometry of methane (CH₄)?
- Linear
- Trigonal planar
- Tetrahedral (Correct answer)
- Octahedral
Correct answer: Tetrahedral
Methane has 4 bonding pairs around the central carbon with no lone pairs (AX₄ by VSEPR theory), giving a tetrahedral geometry with 109.5° bond angles. This is the most stable arrangement for 4 electron pairs.
Question 5: What is the molarity of a solution containing 4 moles of NaCl in 2 liters of solution?
- 8 M
- 0.5 M
- 2 M (Correct answer)
- 4 M
Correct answer: 2 M
Molarity (M) = moles of solute / liters of solution = 4 mol / 2 L = 2 M. Molarity is the most commonly used concentration unit in chemistry.
Question 6: Which of the following is a strong acid?
- Acetic acid (CH₃COOH)
- Hydrochloric acid (HCl) (Correct answer)
- Carbonic acid (H₂CO₃)
- Phosphoric acid (H₃PO₄)
Correct answer: Hydrochloric acid (HCl)
HCl is a strong acid — it completely dissociates in water: HCl → H⁺ + Cl⁻. The six strong acids are: HCl, HBr, HI, HNO₃, H₂SO₄, HClO₄. Acetic acid, carbonic acid, and phosphoric acid are weak acids (partially dissociate).
Tahsili Chemistry 2
What is Le Chatelier's Principle?