Chemistry Video 15 Flashcards
Zeroth Law of thermodynamics
Deals with thermal equilibrium. Describes a situation where there is no net heat flow between 2 systems. If 2 systems are in thermal equilibrium with a third system, then they are also in thermal equilibrium with each other
First Law of thermodynamics
Conservation of energy
Entropy
The partial loss of a heat engine’s ability to do work. State function measured in J/K. Symbol is S
Change in entropy
Heat over the Kelvin temperature for a reversible process. Q / T.
Second law of thermodynamics
The change in entropy of the universe for any spontaneous process is greater than 0. The entropy of the universe must increase for any spontaneous process.
Microstate
A specific configuration of all the particles and energies in a system. The dispersal of matter and energy tends to be spontaneous. Things move to more disorder. S = klnW, where k is the Boltzmann constant 1.38*10^(-23) m^2 kg/s^2 K. W is the number of microstates. The distribution with the greatest number of microstates will be preferred statistically
When change in entropy is a positive value
Increase in entropy, entropically favourable. More likely to be spontaneous.
When change in entropy is a negative value
Decrease in entropy, entropically unfavourable. More likely to be non-spontaneous.
Third law of thermodynamics
At absolute zero (0 K) everything would be a solid. The entropy of any crystalline substance at absolute zero is equal to zero. It is impossible to lower the temperature of any system to absolute zero in a finite number of steps.
Gibbs Free Energy, G
Determines spontaneity. deltaG = deltaH – T*deltaS
Negative deltaG
spontaneous
Positive deltaG
non-spontaneous
deltaG = 0
equilibrium
Standard change in free energy
For equilibrium:
(standard change in free energy) = -(R)(T)(lnK)
Not equilibrium and Q is reaction quotient:
(change in free energy) = (standard change in free energy) + (R)(T)(lnQ)
Standard change in free energy is negative and K > 1
Products favoured (spontaneous)
Standard change in free energy is positive and K < 1
Reactants favoured (non-spontaneous)
Standard change in free energy is 0 and K = 0
Reactants and products favoured equally
From Gibbs Free Energy Equation, delta H is negative and delta S is positive
deltaG is always negative, meaning spontaneous.
From Gibbs Free Energy Equation, delta H is positive and delta S is negative
deltaG is always positive, meaning non-spontaneous.
From Gibbs Free Energy Equation, delta H is positive and delta S is positive
deltaG is spontaneous at high T and non-spontaneous at low T.
From Gibbs Free Energy Equation, delta H is negative and delta S is negative
deltaG is spontaneous at low T and non-spontaneous at high T.
Electric charge
Measured in Coulombs
Electric current
Rate of charge flow carried by electrons or ions. Measured in amperes where 1A = 1 C/s. Always flows in a path called a circuit.
Electric potential
Ability of an electric field to do work (move charges). Measured in volts where 1V = 1 J/C
Electric field
Generated by particles with electric charge
Electrochemistry
Involves REDOX reactions.
Galvanic Cell (AKA voltaic)
Electrochemical cell. Spontaneous REDOX reaction generates an electric current. Each beaker is called a half cell and each half cell has a metal electrode. Oxidation occurs at anode. Reduction occurs at cathode. Half cells are connected by salt bridge that maintains charge balance and by a wire connected to voltmeter. Electrons always go from anode to cathode.
Cell notation
From left to right: list the material in the anode, then put vertical line ( | ) to show phase boundary, then put anode solution including concentration, then put double vertical line ( || ) to represent the separation between the 2 half cells, then put cathode solution including concentration, then put vertical line ( | ) to show phase boundary, list the material in the cathode. Spectator ions not listed. Half reactions have coefficients of 1. Anode always on the left side.
Standard hydrogen electrode
Used as a reference to list reduction potentials for all substances. This is a platinum electrode sitting in 1 molar hydrochloric acid that facilitates reduction of H+ ions into H2 gas, which has a standard reduction potential of 0 V.
Cell potential (E cell)
E cell = E cathode – E anode. When looking at standard reduction potentials of 2 half cells, the half cell reaction with the greater (more positive) reduction potential is the reduction half-reaction, which is the cathode. We do not need to alter the reduction potentials in the list of reduction potentials to calculate E cell.
Primary batteries
Single-use batteries that cannot be recharged. i.e. zinc dry cell, alkaline battery, zinc-carbon battery
Secondary batteries
Multiple-use batteries that can be recharged. i.e. in phones, cars, nickel-cadmium battery, lithium-ion battery, lead acid battery
Fuel cells
Converts chemical energy into electrical energy. For satellites, boats, submarines. Requires continuous source of fuel. Utilize the splitting of hydrogen atoms to produce fuel. The process involves splitting hydrogen into electrons and protons, allowing the
components to run through the battery to produce electricity, and finally combining the
reactants with oxygen to produce water as a byproduct.
Electrolytic cell
An electric current drives a nonspontaneous REDOX reaction. i.e. Electrolysis of water. Electrolysis of aqueous sodium chloride.
Calculate total charge
Current is measured in Amperes. Total charge is Q. Q = It = nF. Q is the total charge in C, I is the current in C/s and t is time in seconds. n is moles of electrons transferred and F is Faraday’s constant of 96485 C/mol.
Equation with Ecell and deltaG
Standard deltaG = -(n)(F)(Ecell)
