How a Salt Forms Flashcards
Define Hess’s Law
If a reaction can take place by more one route, the enthalpy change for the reaction is the same for both routes
Define standard enthalpy of combustion
when 1 mol of a substance is burnt completely in n excess of oxygen under standard conditions
Define standard enthalpy of neutralisation
when an acid and alkali react to form 1 mol of water under standard conditions
Define standard enthalpy change of reaction
when equation quantities of materials react under standard conditions in standard states
Define standard enthalpy of formation
when 1 mol of a substance is formed from its elements in their natural states under standard conditions
What are the standard conditions
298K
101kPa
What does a the cycle look like when you’re given standard enthalpy changes of combustion and a reaction
Reaction given goes along top
Co2 and H2O at the bottom in correct molar quantities from the reactants
Arrows point down from reactants and the products to the CO2 and H2O
What does the cycle look like when you’re given standard enthalpies of formation, and you want to work out the enthalpy change for the combustion of something
Equation given along top
Elements in natural states along the bottom,make sure only 1 mol of product can be formed from them
Arrows pointing up from elements to products and reactants of top equation, ignore oxygen
what is lattice enthalpy
energy released when 1 mole of a crystal is formed from its constituent ions in their gaseous state
what sign will lattice enthalpy have and why
negative
bonds are forming releasing energy
why cant you measure lattice enthalpy directly
cant get gaseous ions separately from the ions of the opposite charge
what is enthalpy of atomisation
enthalpy change when 1 mole of gaseous atoms is formed from the element in its standard state
what is ionisation energy
energy required to remove 1 mole of electrons from 1 mole of gaseous atoms
what is electron affinity
enthalpy change accompanying the gain of 1 mol of electrons by 1 mol of atoms in the gaseous phase
why is the 2nd electron affinity vale for O +
O- ion and electrons are both negative
meaning energy is required to overcome repulsion
what is enthalpy of formation
enthalpy change when 1 mole of a compound is formed from its constituent elements in their standard states
is the lattice enthalpy always positive or negative
negative
what happens to the arrows in a born haber cycle when O- needs another electron added
Requires lots of energy (endothermic), so arrows go down and then back up
what is enthalpy of solution
enthalpy change that occurs when 1 mole of an ionic solid dissolves in water
what is the enthalpy of hydration of an ion
the enthalpy that occurs when 1 mole of a gaseous ion is completely hydrated by water
conditions needed for the hydration of an ion
25oC
101kPa
turning an ionic solid into gaseous ions is known as?
lattice dissociation enthalpy
what does a higher charge density mean
better at attracting water, so more energy released= more exothermic
what does having smaller ions mean
higher charge density, so better at attracting water, so more energy released= more exothermic
what happens as lattice enthalpy increases
more exothermic, so the ionic lattice becomes more stable
what is entropy
a measure of the number of ways that particles can be arranged and the number of ways the energy can be shared out between particles
particles like disorder= more energetically stable
what happens to reactions if disorder increases
they tend to happen spontaneously
what symbol is used to name the amount of energy available due to the arrangement of particles
entropy with the symbol (S)
values of enthalpy and entropy being released
enthalpy- ∆H-ve
entropy- S+ve
enthalpy and entropy units
enthalpy- Kj/mol
entropy- jK-1mol-1
how to calculate ∆Stotal
= ∆Ssystem + ∆Ssurroundings
how to calculate ∆Ssystem
= ∑(entropy of products) - ∑(entropy of reactants)
how to calculate ∆Ssurroundings
= - ∆H/T
enthalpy in j/mol
temp in K
how to calculate ∆Htotal
=∆Hproducts - ∆Hreactants
what is free energy
combines enthalpy and entropy to work out if a reaction is feasible or spontaneous at room temp
symbol for (Gibbs) free energy
G
how to work out ∆G
= ∆H - T∆Ssytem
temp in K
∆S must be in kJ
∆H in kJ
∆G is in kJmol-1
when is a reaction feasible using ∆G
when its negative (energy is given out)
what happens when ∆G = 0
reaction at equilibrium
∆G= ∆H- T∆S
∆H= T∆S
When is a reaction spontaneous
when delta h is more negative than delta s
