UPCAT Chemistry — Chemical Equilibrium & REDOXFlash Cards

What is chemical equilibrium?

A dynamic state where the rates of forward and reverse reactions are equal, and the concentrations of reactants and products remain constant over time. It can only occur in a closed system.

List the 5 characteristics of chemical equilibrium.

1) Occurs only in closed systems 2) All reactants and products are present with unchanged concentrations 3) Forward rate equals reverse rate 4) Can be reached from either direction 5) Shifts when physical conditions change

What is the difference between kinetic energy and potential energy?

Kinetic energy is energy of motion (KE = ½mv² or KE = 3/2RT for gases). Potential energy is stored energy of position. Both are forms of energy that can be converted to work or heat.

Calculate the kinetic energy of a 2 kg object moving at 5 m/s.

Formula: KE = ½mv². Step 1: KE = ½(2 kg)(5 m/s)². Step 2: KE = ½(2)(25) = 25 J. Answer: 25 Joules

Define oxidation and reduction in terms of electrons.

Oxidation is the LOSS of electrons (OIL). Reduction is the GAIN of electrons (RIG). Remember: OIL RIG - Oxidation Is Loss, Reduction Is Gain of electrons.

What is an oxidizing agent and reducing agent?

Oxidizing agent: Species that causes oxidation (gets reduced itself). Reducing agent: Species that causes reduction (gets oxidized itself). The oxidizing agent gains electrons while the reducing agent loses electrons.

What is the oxidation number of oxygen in most compounds?

Oxygen has an oxidation number of -2 in most compounds. Exception: In peroxides (like H₂O₂), oxygen has an oxidation number of -1.

What is the oxidation number of hydrogen in compounds?

Hydrogen is +1 in most compounds. Exception: When bonded to metals in binary compounds (like LiH, NaH, CaH₂), hydrogen has an oxidation number of -1.

Calculate the oxidation number of nitrogen in KNO₃.

Step 1: K = +1, O = -2. Step 2: Sum must equal 0 (neutral compound). Step 3: (+1) + N + 3(-2) = 0. Step 4: +1 + N - 6 = 0. Step 5: N = +5. Answer: +5

Calculate the oxidation number of sulfur in H₂SO₄.

Step 1: H = +1, O = -2. Step 2: Sum must equal 0. Step 3: 2(+1) + S + 4(-2) = 0. Step 4: +2 + S - 8 = 0. Step 5: S = +6. Answer: +6

Balance this REDOX reaction: Al(s) + CuSO₄(aq) → Al₂(SO₄)₃(aq) + Cu(s)

Step 1: Al → Al³⁺ + 3e⁻ (oxidation). Step 2: Cu²⁺ + 2e⁻ → Cu (reduction). Step 3: Balance electrons: 2Al + 3Cu²⁺. Final: 2Al(s) + 3CuSO₄(aq) → Al₂(SO₄)₃(aq) + 3Cu(s)

Identify the oxidizing and reducing agents in: 2H₂(g) + O₂(g) → 2H₂O(g)

Oxidation numbers: H₂ (0 → +1), O₂ (0 → -2). H₂ is oxidized (loses electrons) = reducing agent. O₂ is reduced (gains electrons) = oxidizing agent.

What are the two main methods for balancing REDOX equations?

1) Oxidation Number Method: Use changes in oxidation numbers to balance electrons. 2) Half-Reaction Method: Split into oxidation and reduction half-reactions, balance each separately, then combine.

List the steps for the oxidation number method.

1) Assign oxidation numbers 2) Identify oxidized/reduced species 3) Calculate electrons lost/gained 4) Multiply by factors to equalize electrons 5) Complete balancing by inspection

What is the correct order for balancing atoms in the half-reaction method?

1) Balance atoms other than O and H first 2) Balance oxygen atoms by adding H₂O 3) Balance hydrogen atoms by adding H⁺ 4) Balance charge by adding electrons

Balance this half-reaction in acidic solution: MnO₄⁻ → Mn²⁺

Step 1: Mn balanced. Step 2: Add 4H₂O for O: MnO₄⁻ → Mn²⁺ + 4H₂O. Step 3: Add 8H⁺ for H: MnO₄⁻ + 8H⁺ → Mn²⁺ + 4H₂O. Step 4: Add 5e⁻: MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O

What is the first law of thermodynamics equation?

ΔU = q + w, where ΔU is change in internal energy, q is heat transferred to the system, and w is work done on the system. Energy is conserved in all processes.

Why can dynamic equilibrium only exist in a closed system?

In an open system, reactants or products can escape, preventing the establishment of constant concentrations. A closed system prevents exchange of matter with surroundings, allowing forward and reverse rates to become equal.

What types of reactions are considered REDOX reactions?

1) Formation of compounds from elements 2) All combustion reactions 3) Reactions that generate electricity 4) Reactions that produce cellular energy. All involve net electron transfer between species.

What are the oxidation number rules for Group 1 and Group 2 metals?

Group 1 metals (Li, Na, K, etc.) always have oxidation number +1 in compounds. Group 2 metals (Mg, Ca, Ba, etc.) always have oxidation number +2 in compounds. Aluminum always has +3.