4-4 Reactions that Run to Completion And you

We’ll see later, in equilibrium, that reactions can run in the forward direction and in the reverse direction. However, there are some reactions that predominantly go in the forward direction. These are said to “run to completion” and occurs when product is removed as a gas, solid, or liquid (as shown below):  

Gas Produced FeS(aq) + 2HCl(aq) → FeCl2(aq) + H2S(g) Net Ionic: S-2(aq) + 2H+(aq) → H2S(g)  The product is a gas that leaves the reaction environment.

Solid (ppt) formed NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)   Net Ionic: Ag+(aq) + Cl-(aq) → AgCl(s)

Slightly ionized product (liquid): 2HF(aq) + Ca(OH)2(aq) → 2H2O(l) + CaF2(aq) Net Ionic: 2H+(aq) + 2OH-(aq) → 2H2O(l)  

4-5 Redox Reactions (Section 7.5, 18.1, 18.2, 18.3) Reactions in which one or more electrons are transferred, are called oxidation-reduction reactions or redox reactions. Leo says Ger

L e o Loss of electrons = oxidized G e r Gain of electrons = reduced e-

Oxidation States (Oxidation Numbers) Oxidation numbers provide a way to keep track of electrons in redox reactions, particularly those involving covalent substances. Rules for assigning oxidation states: 1. Element (in natural state) = zero 2. Monatomic ion is same as charge: Na+ = +1 3. Oxygen = -2 ; exception in H2O2 = -1 4. Hydrogen = +1 (exception when w/metal) 5. Sum of oxidation states must equal charge on compound!!!!

Characteristics of Redox Reactions Oxidation states: 2 Na + Cl2 → 2 NaCl Oxidation is an increase in oxidation state, a loss of electrons. Na is oxidized here Reduction is a decrease in oxidation state, a gain of electrons. Cl is reduced here +1 -1 e-

2 Na + Cl2 → 2 NaCl Leo says Ger e- +1 -1 Leo says Ger Sodium is oxidized and chlorine is reduced. Cl2 is the oxidizing agent (electron acceptor). Na is the reducing agent (electron donor). Oxidizing agent is reduced and reducing agent is oxidized!

Oxidation states: CH4 + 2 O2 → CO2 + 2 H2O Now how did that happen????????????? What Is oxidized???? C What is reduced? O2 What is the reducing agent?????? What is the oxidizing agent???? -4 +1 +4 -2 +1 -2 8e-