Definition If oxidation occurs, then reduction must also occur Any chemical process in which elements undergo a change in oxidation number is a Redox reaction

Example 2Na + Cl 2 → 2Na + + 2Cl - This reaction can be thought of as two half reactions 2 Na → 2Na + + 2e oxidation Cl 2 + 2e → 2Cl - reduction These two reactions together are called a redox reaction

Identifying Redox SO 2 + H 2 O + O 2 → H 2 SO 4 NaCl + Ag(NO 3 ) → Na(NO 3 ) + AgCl

Practice Determine if each below is a redox reaction SO 3 + H 2 O → H 2 SO 4 2KNO 3 → 2KNO 2 + O 2 H 2 + CuO → Cu + H 2 O

More Definitions Reducing Agents – elements that undergo oxidation (the cause reduction in another element) Oxidizing Agents – undergo reduction Mg + Cu(NO 3 ) → Cu + Mg(NO 3 ) Mg is reducing agent – being oxidized Cu 2+ is oxidizing agent – being reduced

Corrosion When a metal is reduced When two metals are in contact, the one that is the better reducing agent (most active) will give up electrons to the other one The metal that receives the electrons is reduced – called corrosion

When zinc is wrapped around the Fe nail, Zn is oxidized, so Fe corrodes When copper is wrapped around the Fe nail, Fe is oxidized, so Cu corrodes