Review of Redox Chemistry

Review of Redox Chemistry

by Luis Bello

​Previous Class

​16.1 Spontaneity

16.2 Entropy

16.3 The Second and Third Laws of Thermodynamics

16.4 Free Energy

Multiple Choice

The first law of thermodynamics is a restatement of the

• Zeroth law of thermodynamics
• law of heat addition
• principle of entropy
• conservation of energy

Multiple Choice

When applying the first law of thermodynamics to a system, when is heat a positive quantity?

• when the system does work
• when the system has work done on it
• when the system absorbs heat
• when the system loses heat
• when no work is done either on the system or by the system

Multiple Choice

Which of the following equations is the equation for calculating the work done by a gas in a piston?

• W=Fd

• W=PΔV

• ΔV=Ad

• A=πr²

Multiple Choice

A reaction has both positive ∆S° and ∆H° values. From this information alone, you can conclude that the reaction

• can be spontaneous at any temperature.

• cannot be spontaneous at high temperatures.

• can be spontaneous only at low temperatures.

• can be spontaneous only at high temperatures.

Multiple Choice

Which of the following is not expected to have a value of zero at 25°C and 1 atm?

• ∆H°_f for F_{2 (g)}

• ∆G°_f for Li_(s)

• S° for Fe_(s)

• ∆H°_f for Mg_(s)

Multiple Choice

Consider this hypothetical reaction (at 375 K). The free energies in kJ/mol at this temperature are given below each substance in parentheses. What is the value of Gibbs free energy for the reaction at this temperature? Is the reaction spontaneous?

• -300.0 kJ; spontaneous

• 0.00 kJ; at equilibrium

• 300.0 kJ; non-spontaneous

• 600.0 kJ; non-spontaneous

Multiple Choice

A certain non-spontaneous reaction has ∆H of 12.3 kJ and a ∆S of 42 J/K. At approximately what temperature would the reaction become spontaneous?

• -20°C

• 0°C

• 20°C

• 100°C

Multiple Choice

Which of the following is true when ice melts?

• ∆H<0 ∆S<0

• ∆H=0 ∆S=0

• ∆H<0 ∆S>0

• ∆H>0 ∆S>0

​Redox Chemistry

​Learning Objectives

​

By the end of this section, you will be able to:

• Describe defining traits of redox chemistry

• Identify the oxidant and reductant of a redox reaction

• Balance chemical equations for redox reactions using the half-reaction method

​Oxidation Numbers

​By definition, a redox reaction is one that entails changes in oxidation number (or oxidation state) for one or more of the elements involved.

​

​

​

​

​There are 2 methods

​1- Oxidation numbers

​

​

​2- Half-reaction method

​

​Balancing using the oxidation number

​half-reaction method

​

1. Write skeletal equations for the oxidation and reduction half-reactions.

2. Balance each half-reaction for all elements except H and O.

3. Balance each half-reaction for O by adding H₂O.

4. Balance each half-reaction for H by adding H⁺.

5. Balance each half-reaction for charge by adding electrons.

6. If necessary, multiply one or both half-reactions so that the number of electrons consumed in one is equal to the number produced in the other.

7. Add the two half-reactions and simplify.

8. If the reaction takes place in a basic medium, add OH⁻ ions the equation obtained in step 7 to neutralize the H⁺ ions (add in equal numbers to both sides of the equation) and simplify.

​

Balancing Equations for Redox Reactions in Acidic Solutions

​

Write the balanced equation representing reaction between solid copper and nitric acid to yield aqueous copper(II) ions and nitrogen monoxide gas.

​​Balancing Equations for Redox Reactions in Basic Solutions

Write the balanced equation representing reaction between aqueous permanganate ion,MnO₄⁻, and solid chromium(III) hydroxide, Cr(OH)₃, to yield solid manganese(IV) oxide, MnO₂, and aqueous chromate ion,CrO₄²⁻CrO₄²⁻The reaction takes place in a basic solution.

Home

Open in new tab

Copy link