Energetics Flashcards
Define enthalpy of formation
Enthalpy change when one mole of substance is formed from its constituent elements with substances in standard states
Define enthalpy of combustion
Enthalpy change when one mole of a substance undergoes complete combustion in oxygen with substances in standard states
Define enthalpy of neutralisation energy
Enthalpy change when 1 mole of water is formed in a reaction between acid and alkali under standard conditions
Define first ionisation enthalpy
Enthalpy change when each atom in a mole of gaseous atoms loses one electron to form one mole of gaseous 1+ ions
Define first electron affinity
Enthalpy change when one each atom in one mole of gaseous atoms gains one electron to form one mole of gaseous 1- ions
Define enthalpy of atomisation
Enthalpy change when one mole of gaseous atoms is produced from an element in its standard state
Define hydration enthalpy
Enthalpy change when one mole of gaseous ions becomes hydrated (dissolved in water)
Define enthalpy of solution
Enthalpy change when one mole of ionic solid dissolved in an amount in water large enough that the dissolved ions are seperated
Define bond dissociation enthalpy
Enthalpy change when one mole of covalent bonds are broken in the gaseous state
Define lattice enthalpy of formation
Enthalpy change when one mole of solid ionic compound is formed from its gaseous constituent ions
Define lattice enthalpy of dissociation
Enthalpy change when one mole of a solid ionic compound is broken up into its gaseous constituent ions
Define enthalpy of vapourisation
Enthalpy change when one mole of a liquid is turned into a gas
Define enthalpy of fusion
Enthalpy change when one mole of a solid is turned into a liquid
What is a born-Haber cycle
Represents the energy change through a reaction
Enthalpy change equation
Enthalpy change is bonds broken - bond broken
Factors affecting lattice enthalpy
Ionic charge- the higher the charge on the ion, the stronger the electrostatic attraction and hence more energy released when bond formed
Ions radii- the smaller the ionic radii, the closer the electrons sit together, the stronger the attraction and the more exothermic the lattice enthalpy
Factors affecting enthalpy of hydration
Ionic charge- the higher the charge, the stronger the attraction to the polar water molecules, the stronger the electrostatic attraction and hence the more energy released
Ionic radii- smaller ions have a higher charge density, meaning they attract water molecules more and have more exothermic enthalpy
What is the entropy
The measurement of disorder
How does entropy change across states
Solid has lowest enthalpy, water has middling and gas the highest
When is there zero entropy
At absolute zero
What is Specific heat capacity and it’s equation
The energy required (in joules) to raise the temp of 1g of substance by 1K
E= mc delta T
What is the quanta
The package of energy
Name the three types of molecular movement
Translation- molecules moving one place to another
Rotation- molecules spinning
Vibration- bonds stretching and compressing
The order of quanta size
Vibration > rotation > translation
How does heating affect entropy
Heating increases the total number of quanta, increasing the possible orders, increasing entropy
When will entropy increase
Heating
Reduced pressure
More molecules
Physical state
What is a spontaneous reaction
A physical or chemical change that occurs with no outside intervention
NOTE: energy may be initially supplied
When is a reaction feasible
Total entropy change is +ve
Second law of thermodynamics
For a spontaneous process, the total entropy change in a system and it’s surroundings will increase
Equation for Change in entropy of surroundings
Delta S surroundings = negative delta H/ T
Delta S surroundings measured in JKmol-1
Delta H measures d in kJmol-1
T measured in K
What does Gibbs free energy change tell us and what is it’s symbol
Delta G
Tells us if a reaction is feasible
Equation for Gibbs free energy
Delta G = delta H minus T delta system
If the enthalpy change is exothermic and entropy change is increased, is the reaction feasible
Yes Gibbs free energy is always negative
If the enthalpy change is exothermic and entropy change is decreased, is the reaction feasible
Only feasible at low temperatures
If the enthalpy change is endothermic and entropy change is increased, is the reaction feasible
Only feasible at high temperatures
If the enthalpy change is endothermic and entropy change is decreased, is the reaction feasible
Never feasible, delta G always positive
Key rule for Gibbs feee energy
Is delta G < 0, the reaction is feasible
Equation for delta H in terms of Q
Delta H = (Q/1000) / moles reacted
