3.6 - Enthalpy change for solids + structures

Question 1

First law of thermodynamics?

Answer 1

Energy cannot be created nor destroyed, only transferred from one form to another

Question 2

what is the affect of this?

Answer 2

possible to measure the energy change in a chemical reaction

Question 3

Hess’s law?

Answer 3

total enthalpy change for a reaction
from reactants to products is independent of the route taken.

Question 4

Enthalpy change of a reaction?

Answer 4

a measure of the energy change of a reaction
must be under standard conditions
298 K
1 atm
1.01 x 10 ^5 kPa
25 degrees

Question 5

Standard state?

Answer 5

physical state of a substance under standard conditions

Question 6

Standard enthalpy change of atomization?

Answer 6

the enthalpy change when 1 mole of atoms of an element in the gs phase is formed from the elements in its standard state under standard conditions

Question 7

Atomization?

Answer 7

when you turn a solid into a gas
Na(s) —- Na(g)
positive
endothermic

Question 8

Standard enthalpy change of lattice formation?

Answer 8

enthalpy change when 1 mole of ionic compound is formed from ions of the elements in the gas

e.g Na +(g) + Cl-(g —– NaCl

Question 9

Lattice breaking?

Answer 9

reverse of formation + its the enthalpy change between 1 mole of an ionic compound = broken up into ions of the elements in the gas phase
NaCl(s) —- Na+(g) + Cl- (g)

Question 10

Standard enthalphy of hydration?

Answer 10

1 mole of an ionic compound in solution formed from ions of the elements in the gas phase
aq + Na+(g) + Cl-(g) —- NaCl(g)

Question 10

What is positive and negative?

Answer 10

formation = positive
atomization = negative
hydration = negative

Question 11

Electron affinity?

Answer 11

enthalpy change when 1 mole of gaseous negative ions are formed from fas atoms by gaining an electron
Cl(g) + e- —– Cl-

Question 12

Ionization?

Answer 12

when 1 mole of gaseous positive ions is formed from gas atoms by losing an electron

Na(g) — Na+ + e-

Question 13

Valence?

Answer 13

outside

Question 14

Covalent?

Answer 14

shared pair of electrons

Question 15

Enthalpy change of solution?

Answer 15

ionic substances consist of a lattice of positive and negative ions held together by electrostatic forces.
To dissolve the ionic substances, the forces between the ions must be broken and replaced by alternative forces
water is polar as the O2 atoms are delta negative and delta positive

Question 16

Standard enthalpy change of solution?

Answer 16

enthalpy when 1 mole of a substance dissolves completely in a solvent under standard conditions to form a solution

Question 17

Enthalpy change of a solution?

Answer 17

lattice breaking + hydration

Endo thermic + exothermic

Question 18

If the lattice of Hydration is greater than the lattice breaking?

Answer 18

salt dissolves

Question 19

If hydration is less than breaking?

Answer 19

salt will not dissolve

Question 20

Stability of compounds?

Answer 20

if enthalpy change of formation is negative
Energy given out as the compound is formed from its elements
This means the compound is stable
If delta H formation is positive, the compound is unstable with respect to its elements
This doesn’t mean it cannot exist, but it requires energy to change the elements into compounds