Chem Exam 4

Terms and Equations

First Law of Thermodynamics

the internal energy of a system changes through heat exchange with the surroundings or work on or by the system

Enthalpy (∆𝐻)

the heat flow for a process at constant pressure

state function

its value depends only on the state of a system, and not the path taken to reach that state

Exothermic

meaning that thermal energy is transferred from the system to its surroundings

Endothermic

meaning that thermal energy is transferred to the system from its surroundings

Hess’s Law

if a process can be written as the sum of several stepwise processes, the enthalpy change of the total process equals the sum of the enthalpy changes of the various steps

standard state

pure (s) and (ℓ), pressure 1atm (g), concentration 1M (aq), and T=298K

Spontaneous process

process that takes place without a continuous input of energy from an external source

Nonspontaneous process

process that requires continual input of energy from an external source

entropy (S)

measure of the disorder of the system

Microstate

possible configuration or arrangement of matter and energy within a system

Second Law of Thermodynamics

all spontaneous processes involve an increase in the entropy of the universe

Gibbs free energy change

thermodynamic property defined in terms of system enthalpy and entropy

Standard Entropy

entropy for one mole of a substance at 1 atm* pressure; tabulated values are usually determined at 298.15 K

Electrochemistry

The presence and flow of electrical charge

Galvanic Cells (voltaic cells)

the electrochemical cells in which spontaneous oxidation- reduction reactions produce electrical energy.

anode

where the oxidation reaction occurs

cathode

where the reduction reaction occurs

When a complete circuit is formed, electrons travel …

up the wire from the anode

After passing through the external circuit and doing work for us, the electrons

reduce ions at the cathode

To determine the temperature for transition to spontaneous process by …

setting ΔG° = 0

active electrode

When the anode and cathode materials participate in the reactions

inert electrode

are sometimes needed to complete the circuit when a half-reaction does not contain an active electrode

standard hydrogen electrode

serves as the reference for all half-cell potential values with an assigned value of 0 V for the oxidation reaction

Electrolysis

process using electrical energy to cause a nonspontaneous process to occur

Electrolytic cell

electrochemical cell in which an external source of electrical power is used to drive an otherwise non spontaneous process

the strongest oxidizing agent has the …

highest E°

the strongest reducing agent has the …

lowest E°

What is the symbol for the standard cell potential?

E°_cell

Corrosion (Electrochemical degradation of materials through spontaneous oxidation) can be limited by …

1) Alloying

2) Barriers

3) Sacrificial anode

Chloralkali Process

Aqueous sodium chloride can be electrolyzed to produce NaOH (aq) and Cl2(g)

Hall–Héroult process

A molten mixture of aluminum ore (bauxite, Al2O 3) and cryolite (Na 3AlF 6) are electrolyzed at (>900°C) to produce very pure aluminum metal

Primary cell

non-rechargeable battery, suitable for single use only

Secondary cell

battery designed to allow recharging

Fuel cell

galvanic cells that require a continuous feed of redox reactants

Batteries

single or series of galvanic cells designed for use as a source of electrical power

Corrosion

degradation of metal via a natural electrochemical process; always oxidation (anode reaction).

oxidation number of a monatomic ion is equal to

the ion’s charge