Chemistry · Ch 6 — Redox Reactions
Introduction
Introduction
Redox is a short form for the two words 'oxidation' and 'reduction' occurring together in one reaction. Redox reactions are not a rare, specialised topic -- they run through everyday life. Respiration, the process by which our bodies extract energy from food, is a redox reaction. Rusting, the slow corrosion of iron exposed to air and moisture, is a redox reaction. The combustion of any fuel -- wood, cooking gas, petrol -- is a redox reaction. Even smaller, more subtle changes are redox at heart: a freshly cut apple turning brown on exposure to air is oxidation of compounds in the apple by atmospheric oxygen, a car's metal bumper losing its shine over the years is a slow oxidation (corrosion) of the metal, and an old battery finally going flat reflects that the redox reaction generating its current has essentially run to completion, leaving little further chemical driving force. Because so much of chemistry (and biology) is redox chemistry, this chapter builds up, step by step, a precise and general way to recognise a redox reaction, to identify which species is oxidised and which is reduced, and to balance the equation for one -- starting from the oldest, simplest ideas about oxidation and reduction and ending with the modern oxidation-number method and the two standard techniques used to balance any redox equation.
Worked out. A chapter-opening reflection box posing three everyday questions for students to ponder before the formal content begins: why does a cut apple turn brown when exposed to air; why does an old car's metal bumper change colour over time; and why do new batteries eventually become useless after some days. These are rhetorical hook questions (browning is an oxidation of compounds in the apple by atmospheric oxygen, bumper corrosion is rusting, and a battery going flat reflects its internal redox reaction running to completion) meant to motivate the chapter rather than to be answered and submitted.
Hook-1: Can you tell? (everyday redox questions).
Worked out. A second reflection box recalling material from earlier classes before the chapter proceeds: what is a combustion reaction, an equation for the combustion of methane, and what the driving force behind reactions of elements is. This primes students with the basic 'element + oxygen' combination idea (combustion) that Section 6.1.1 immediately builds on when it defines oxidation classically as combination with oxygen.
Hook-2: Can you recall? (prior-knowledge questions).