Chapter 22 Enthalpy And Entropy Flashcards
What is the enthalpy change of formation?
The enthalpy change that occurs when one mole of a compound is formed from its elements in their standard states under standard conditions
What is the enthalpy change of combustion?
The enthalpy change that occurs when one mole of a substance is completely combusted in oxygen under standard conditions
What is the enthalpy change of neutralisation?
The enthalpy change that occurs when one mole of water is formed during a neutralisation reaction between an acid and an alkali under standard conditions
What is the enthalpy change of a reaction?
The enthalpy change when a chemical reaction occurs under standard conditions in the stoichiometric ratios of the balanced equation
State whether the enthalpy change of formation is endothermic or exothermic
Exothermic
What is enthalpy change of atomisation?
The enthalpy change that occurs when one mole of gaseous atoms are formed from its elements in their standard states under standard conditions
State whether the enthalpy change of atomisation is endothermic or exothermic
Endothermic
What is bond enthalpy?
The enthalpy change when one mole of a covalent bond is broken in the gaseous state
State whether bond enthalpy is endothermic or exothermic
Endothermic
What is first ionisation energy?
The enthalpy change that occurs when one mole of electrons are removed from one mole of gaseous atoms to produce one mole of gaseous +1 ions
State whether first ionisation energy is endothermic or exothermic?
Endothermic
What is second ionisation energy?
The enthalpy change that occurs when one mole of electrons are removed from one mole of gaseous +1 ions to produce one mole of gaseous 2+ ions
State whether second ionisation energy is endothermic or exothermic
Endothermic
What is first electron affinity?
The enthalpy change when each atom in one mole of gaseous atoms gains one electron to form one mole of gaseous 1- ions under standard conditions
State whether first electron affinity is endothermic or exothermic
Exothermic
What is second electron affinity?
The enthalpy change that occurs when each ion in one mole of gaseous 1- ions gains one electron to form one mole of gaseous 2- ions under standard conditions
State whether second electron affinity is endothermic or exothermic
Endothermic
What is hydration enthalpy?
The enthalpy change when one mole of gaseous ions become hydrated (dissolved in water) under standard conditions
What is enthalpy of solution?
The enthalpy change when one mole of an ionic solid dissolves in an amount of water large enough so that the dissolved ions are well separated and do not interact with each other under standard conditions
What is lattice enthalpy?
The enthalpy change when one mole of a solid ionic compound is formed from its constituent ions in the gas phase under standard conditions
State whether lattice enthalpy is endothermic or exothermic
Exothermic
What factors can affect lattice enthalpies?
The greater the ionic charge the more exothermic the lattice enthalpy will be because there is a stronger attraction between ions
The smaller the ionic radius the more exothermic the lattice enthalpy because there is a stronger attraction between ions
What is entropy?
A measure of the dispersal of energy
Also known as the measure of disorder
How does entropy change with the level of disorder?
The higher level of disorder = the higher entropy
The lower level of disorder = the lower entropy
How do entropy values change with the different physical states?
From solids —> liquids —> gases
Entropy increases because gases are more disordered
What is the symbol used for entropy?
S
What are the units of entropy?
JK-1mol-1
How does entropy change with temperature?
As temperature increase entropy will also increase as the level of disorder increases
Predict whether the entropy value will increase or decrease
LiCO3 (s) —> Li2O (s) + CO2 (g)
The entropy will increase because there is more disorder on the products side.
This is because Li2CO3 (s) forms Li2O (s) and CO2 (g) - there are two products formed including a gas which shows there will be a higher degree of disorder.
Predict whether the entropy value will increase or decrease
SO2 (g) + 2H2S (g) —-> 3S (s) + 2H2O (g)
The entropy will decrease because there are 3 mole of gas on reactant and only 2 moles of gas on products alongside 3 moles of a solid showing that there is a higher degree of disorder on the reactants side.
How is entropy calculated?
∆S = ∑(entropies of products) — ∑ (entropies of reactants)
State whether the enthalpy of hydration is endothermic or exothermic
Exothermic
State whether the enthalpy of solution is endothermic or exothermic
Can be exothermic or endothermic
When does the enthalpy change of solution become endothermic
When the Lattice enthalpy > ∑ enthalpy change of hydration
When does the enthalpy change of solution become exothermic
When the ∑ enthalpy change of hydration > lattice enthalpy
State the factors that can affect lattice enthalpy and enthalpy of hydration
Ionic radius
Ionic charge
How does the lattice enthalpy become more exothermic?
The smaller the ionic radius, the greater attraction between the ions
The greater the ionic charge, the greater attraction between the ions
The more exothermic the lattice enthalpy
How does the enthalpy of hydration become more exothermic?
The smaller the ionic radius, the stronger the attraction between the ions and water molecule
The greater the ionic charge, the stronger the attraction between the ions and water molecules
The more exothermic the hydration enthalpy
What is Gibbs Free energy ∆G
Used to tell whether a process is feasible or not at a given temperature
When is a process feasible according to ∆G?
The process is feasible at a given temperature if
∆G is negative or equal to zero
How is ∆G calculated?
∆G = ∆H — T ∆S
∆H = kJmol-1
∆G = kJmol-1
T= kelvin
∆S= JK-1mol-1 (IMPORTANT NEEDS TO BE CONVERTED INTO KJ SO DIVIDE BY 1000)
What is the equation of ∆G when calculating the temperature at which a process is feasible?
T= ∆H/ ∆S
What are the limitations when making predictions based off ∆G?
∆G for a process may be less than zero at a given temperature but the activation energy is too high for the reaction to proceed.
