Redox Overview

AUTO-OXIDATION

Some species can act as oxidants and reductants. In special cases, this means the species can decompose itself: auto-oxidation.

KEY CONCEPTS

EQUATIONS

Oxidation Numbers

A quicker way to justify that redox has occurred is to assign atoms their oxidation numbers. If the oxidation number has changed, it is redox:

Redox Half Equations

One of the most important skills we need to have is to write half equations. Once we know which species is being oxidised (or reduced) and which species it has become, we can start to build a half equation using some useful steps/rules:

The following videos are overviews of oxidation and reduction but also include how to write balanced half equations from about the 4-minute mark:

Practical Redox

The following video shows the results of a couple of our experiments for today:

For each reaction:

1. Identify the redox pairs. For example, Permanganate ions and Manganese ions are a pair.
2. Write the half equations for each redox pair.
3. Combine the half equations to give an overall (net) equation.
4. Use oxidation numbers to justify that these are indeed redox reactions. In the first experiment, focus on the oxidation numbers of manganese and iron. In the second experiment, look at the oxidation number of chromium.

Oxidation Reduction Intro

We were introduced to a special type of reaction: Oxidation-Reduction (Redox). What are these reactions? How do we tell if a reaction is redox?

Here are some key terms that we discussed. Understanding and being able to use these terms will help us in the upcoming Achievement Standard assessment tasks.

Calculating Enthalpy Change from Experimental Results

We looked at two possible ways. They are different, depending upon the data you have been given.

Using a Standard Solution

• Precisely known concentration
• Precisely known volume (therefore, known mass as well)
• Known temperature change

Using a Pure Solid

• Precisely known mass of solid
• Known mass of solution
• Known temperature change

Bond Energies

To try and bring everything together, we have to decide if some common reactions/changes are exothermic or endothermic and explain how we chose:

Enthalpy Change Graphs

CATALYSTS

LOWER INITIAL TEMPERATURE

HIGHER INITIAL TEMPERATURE

Enthalpy Changes

We did some experiments to show that some reactions release heat energy (observed as a temperature increase) while others absorb heat energy (temperature decrease). This is explained using a concept called enthalpy.