Thermodynamics Flashcards
What is the symbol for enthalpy change?
What is the definition of enthalpy change?
What are the standard conditions for an enthalpy change that was measured under standard conditions?
Delta H
The heat energy transferred in a reaction at constant pressure
298 K and 100 kPa.
Describe exothermic reactions
Have a negative delta H value because heat energy is given out
Describe endothermic reactions
Have a positive delta H value because heat energy is absorbed
Enthalpy change of formation
The enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions
Bond dissociation enthalpy
The enthalpy change when all the bonds of the same type in 1 mole of gaseous molecules are broken
Enthalpy change of atomisation of an element
The enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard state
Enthalpy change of atomisation of a compound
The enthalpy change when 1 mole of a compound in its standard state is converted to gaseous atoms
First ionisation energy
The enthalpy change when 1 mole of gaseous 1+ ions is formed from 1 mole of gaseous ions
Second ionisation energy
The enthalpy change when 1 mole of gaseous 2+ ions is formed from 1 mole of gaseous 1+ ions
First electron affinity
The enthalpy change when 1 mole of gaseous 1- ions is formed from 1 mole of gaseous atoms
Second electron affinity
The enthalpy change when 1 mole of gaseous 2- ions is formed from 1 mole of gaseous 1- ions
Enthalpy change of hydration
The enthalpy change when 1 mole of aqueous ions is formed from 1 mole of gaseous ions
Enthalpy change of solution
The enthalpy change when 1 mole of solute is dissolved in enough solvent that no further enthalpy change occurs on further dilution
Lattice enthalpy of formation
Is it an exothermic or endothermic reaction?
The enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions under standard conditions
Exothermic
Lattice enthalpy of dissociation
Is it an exothermic or endothermic reaction?
The enthalpy change when 1 mole of a solid ionic compound is completely dissociated into its gaseous ions under standard conditions
Endothermic
What is lattice enthalpy a measure of?
Ionic bond strength
Two definitions of entropy
The number of ways that particles can be arranged
The number of ways that the energy can be shared out between the particles
The more disordered the particles are…
What does a large positive value of entropy show?
The higher the entropy is
A high level of disorder
In entropy, more particles means…
Why is this?
More entropy
Entropy increases because the number of moles increases
Feasible reaction
Reactions that happen by themselves without the addition of energy
What is the symbol for entropy change?
What is the equation for calculating entropy change?
Delta S
Entropy change= Entropy of products - Entropy of reactants
Standard entropy of a substance (with numbers)
The entropy of 1 mole of that substance under standard conditions (pressure of 100 kPa and temperature of 298 K)
Symbol for free energy change
Definition for free energy change
Equation for calculating free energy change
Give units
Delta G
A measure used to predict whether a reaction is feasible
Delta G= Delta H - ( T x Delta S)
Delta G= J mol -1
Delta H= J mol -1
T= K
Delta S= J K -1 mol -1
If Delta G is negative or equal to zero…
The reaction might happen by itself (ie feasible)
Describe reactions that are feasible at any temperature
If a reaction is exothermic (negative delta H) and has a positive entropy change, then delta G is always negative since Delta G= Delta H - ( T x Delta S)
Describe reactions that are not feasible at any temperature
If a reaction is endothermic (positive delta H) and has a negative entropy change, then delta G is always positive
What happens in a reaction if delta H is positive (endothermic) and delta S is positive?
The reaction won’t be feasible at some temperatures but will be at a high enough temperature
What happens in a reaction if delta H is negative (exothermic) and delta S is negative?
The reaction will be feasible at lower temperatures but won’t be feasible at higher temperatures
When is a reaction just feasible?
Equation for calculating temperature at which a reaction becomes feasible
When delta G is zero
T= Delta H -:- Delta S
T= enthalpy change -:- entropy change
