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44 Cards in this Set
- Front
- Back
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Lattice enthalpy
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The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions
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What is the sign of lattice enthalpy and why?
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It is always NEGATIVE because it is an exothermic change. Energy is GIVEN OUT when ionic bonds are being formed from gaseous ions
A LARGE NEGATIVE VALUE indicates strong electrostatic forces of attraction between bonds |
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Define Hess' Law
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If a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route
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Enthalpy change of formation
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The enthalpy change that takes place when one mole if a compound is formed from its constituent elements in their standard conditions
It's usually EXOTHERMIC |
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Enthalpy change of atomisation
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The enthalpy change that takes place when one mole of gaseous atoms forms from the element in its standard state
It's always ENDOTHERMIC as bonds have to be broken |
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First ionisation energy
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The enthalpy change accompanying the removal of one electron from each atom in one mole of gaseous atoms to form one mole if gaseous 1+ ions
This is ENDOTHERMIC because the electron being lost has to overcome attraction from the nucleus in order to leave the atom |
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Second ionisation energy
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The enthalpy change accompanying the removal of one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions. This is MORE ENDOTHERMIC as the electron being lost is closer to the nucleus
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First electron affinity
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The enthalpy change accompanying the addition of one electron to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions
This is EXOTHERMIC as the electron is attracted into the outer shell of an atom by the nucleus |
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Second electron affinity
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The enthalpy change accompanying the addition of one electron to each ion in one mole of gaseous 1- ions to form one mole of gaseous 2- ions
This is an ENDOTHERMIC process because the electron is repelled by the 1- ion which has to be overcome |
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Born Haber cycles calculations
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Enthalpy of formation equals sum of all other enthalpy changes, rearrange to get lattice enthalpy
Remember to multiply by two if necessary |
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Enthalpy change of solution definition
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The enthalpy change that takes place when one mole of a compound is completely dissolve in water under standard conditions.
Can be exothermic or endothermic. It produces the aqueous ions. |
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What happens when a solid dissolves (two processes)?
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Breakdown of the ionic lattice into gaseous ions - this is endothermic as energy is required to overcome attractive forces between oppositely charge ions
Hydration of the ions |
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Enthalpy change of hydration definition
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The enthalpy change that takes place when one mole of isolated gaseous ions is dissolved in water forming one mole of aqueous ions under standard conditions
This is EXOTHERMIC as energy is released when ions form bonds with water |
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Lattice enthalpy calculations using hydration and solution
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Remember enthalpy change of solution can be either positive or negative
Hydration enthalpies = lattice enthalpy + enthalpy of solution |
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What affects lattice enthalpy (two reasons and how)
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IONIC SIZE - as ionic radius increases, attraction between ions decrease and lattice enthalpy becomes less exo
IONIC CHARGE - as charge increases, greater attraction between ions and ionic radius decreases so enthalpy is more exo |
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What affects enthalpy of hydration (two things and how)
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IONIC SIZE- as radius increases, hydration becomes less exothermic as there is less attraction for the water molecules and less energy released
IONIC CHARGE- as size decreases and charge increases, there is greater attraction for the water molecules so more exo |
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Define entropy
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The quantitative measure of the degree of disorder in a system, it is ALWAYS POSITIVE as particles are in constant motion
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Calculating entropy changes
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Products - reactants
If the change makes the system more random, then it is positive Measured in joules per mole |
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Born Haber cycles calculations
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Enthalpy of formation equals sun of all other enthalpy changes, rearrange to get lattice enthalpy
Remember to multiply by two if necessary |
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If H is negative and S positive, then G is...
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Always negative, and reaction is feasible
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Enthalpy change of solution definition
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The enthalpy change that takes place when one mole of a compound is completely dissolve in water under standard conditions.
Can be exothermic or endothermic. It produces the aqueous ions. |
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What happens when a solid dissolves (two processes)?
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Breakdown of the ionic lattice into gaseous ions - this is endothermic as energy is required to overcome attractive forces between oppositely charge ions
Hydration of the ions |
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Enthalpy change of hydration definition
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The enthalpy change that takes place when one mole of isolated gaseous ions is dissolved in water forming one mole of aqueous ions under standard conditions
This is EXOTHERMIC as energy is released when ions form bonds with water |
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Lattice enthalpy calculations using hydration and solution
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Remember enthalpy change of solution can be either positive or negative
Hydration enthalpies = lattice enthalpy + enthalpy of solution |
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What affects lattice enthalpy (two reasons and how)
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IONIC SIZE - as ionic radius increases, attraction between ions decrease and lattice enthalpy becomes less exo
IONIC CHARGE - as charge increases, greater attraction between ions and ionic radius decreases so enthalpy is more exo |
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What affects enthalpy of hydration (two things and how)
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IONIC SIZE- as radius increases, hydration becomes less exothermic as there is less attraction for the water molecules and less energy released
IONIC CHARGE- as size decreases and charge increases, there is greater attraction for the water molecules so more exo |
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Define entropy
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The quantitative measure of the degree of disorder in a system, it is ALWAYS POSITIVE as particles are in constant motion
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Calculating entropy changes
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Products - reactants
If the change makes the system more random, then it is positive Measured in joules per mole |
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Free energy change definition
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The balance between entropy, enthalpy and temperature process. 🔼G = 🔼H - T🔼S
A reaction is spontaneous when 🔼G is less than zero |
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If H is negative an S negative then G is...
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Negative at low temperatures so reaction is feasible at low temperatures
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If H is negative an S negative then G is...
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Negative at low temperatures so reaction is feasible at low temperatures
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If H is positive and S positive then G is ....
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Negative at high temperatures, so reaction is feasible at high temperatures
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If H is negative an S negative then G is...
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Negative at low temperatures so reaction is feasible at low temperatures
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If H is positive and S positive then G is ....
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Negative at high temperatures, so reaction is feasible at high temperatures
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How do endothermic reactions take place spontaneously?
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S must be positive and the temperature must be high enough so that T🔼S> 🔼H
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If H is negative an S negative then G is...
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Negative at low temperatures so reaction is feasible at low temperatures
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If H is positive and S positive then G is ....
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Negative at high temperatures, so reaction is feasible at high temperatures
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How do endothermic reactions take place spontaneously?
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S must be positive and the temperature must be high enough so that T🔼S> 🔼H
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Working out minimum temperature for a reaction to be feasible
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Calculate T when 🔼G is zero
T = 🔼H / 🔼S |
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If H is negative an S negative then G is...
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Negative at low temperatures so reaction is feasible at low temperatures
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If H is positive and S positive then G is ....
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Negative at high temperatures, so reaction is feasible at high temperatures
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How do endothermic reactions take place spontaneously?
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S must be positive and the temperature must be high enough so that T🔼S> 🔼H
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Working out minimum temperature for a reaction to be feasible
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Calculate T when 🔼G is zero
T = 🔼H / 🔼S |
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Converting between Celsius and K
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To convert degrees to K, add 273
To convert K to degrees, subtract 273 298K is room temperature |
