Topic 5/15

Question 1

Standard enthalpy of formation, which equation do you choose?

Answer 1

Has to make ONE mole of product so coefficent should be one

Question 2

Limitations of calorimetry

Answer 2

Heat loss to surroundings,

Assumes mass and specific heat capacity of aqueous solutions are equal to that of water, but valid because these values for water used are higher than most other substances

Density of solution is 1.00g
Specific heat capacity is 4.18, that of pure water

Reaction goes to complettion
Reactants do not react with other substances

Question 3

Why is cycle significant for ozone vs oxygen destruction?

Answer 3

Ozone weaker so breaks easier, oxygen requires more energy to break so absorbs more of the harmful uv light (242nm)

Ozone abosrbs lower frequency, longer wavelength of light

Only the shorter wavelength which is less damaging radiation reaches the earth’s surface

Question 4

Define lattice enthalpy

Answer 4

The enthalpy change when 1 mole of ionic lattice dissolve sri form gaseous ions

MX (s) = M+ (g) + X- (g)

Question 5

How to calculate enthalpy changes for the dissolution of solids?

enthalpy change of solution

Answer 5

Enthalpy change of solution = (enthalpy change of hydration for each ion) + (lattice enthalpy)

Question 6

What sign is teh enthalpy of solution for a soluable solution

Answer 6

Negative or slightly positive

enthalpy of solution needs to be exo

Question 7

How to determine if reaction is spontaenous with delta s and h

Answer 7

Construct graph and top left spon, top right, spon with high temps, bottom left spon with low temp, and bottom right always non

Question 8

Equation for enthalpy of solution

Answer 8

Enthalpy of solution = enthalpies of hydration + lattice enthalpy

Question 9

Equation for lattice enthalpy

Answer 9

MX(s) = M+ (g) + X- (g)

Question 10

Specific heat capacity definition

Answer 10

Amount of heat absorbed when material increases by one degree

Question 11

With equal masses and energy absorbed, which substance’s temperature increases by less?

Answer 11

The one with higher heat capacity because it takes more energy to increase the heat

Question 12

Enthalpy of products increase or decrease for endothermic

Answer 12

Increases because absorbed heat

Question 13

Define enthalpy of formation

Answer 13

Enthapy change when on emole of compound formed from elements in standard states (likely solid)

Question 14

Equations for enthalpy of formation

Answer 14

Hf = Hf (products) - HF reactants
Hf = Hc (reactants) - Hc (products)

Question 15

Equations for enthalpy of combustion

Answer 15

Hc = Hc (reactatnts) - Hc (products)
Hc = Hf (products) - Hf (reactants

Question 16

Enthalpy products or reactants

Answer 16

ALWAYS products - reactants (2-1) except for bond enthalpies and combustion

Question 17

Deduce change in enthalpy when 56.00g of ethanol burned. Describe how you would do this

Answer 17

Find moles of ethanol and multiply that by the enthalpy of combustion of ethanol

but make sure no negative

Question 18

How to determine which compound has the highest lattice enthalpy

Answer 18

The one with the strongest bonds, ions with larger charge but less valence shells

Question 19

Born Haber Cycle Formula:

Order on cyce chart

Answer 19

Latice = Atomization + E (bond dissociation) + IE (ionization energy) + EA (electron affinity) - F (formation)

L = AEI(EA)F

FAEIE

Question 20

Which system has the most negative entropy change?

Answer 20

When gaseous particles go from more to less, more ordered so negative entropy change

Question 21

Solubility changes with temperature depending on endo and exothermic

Answer 21

Endothermic - solubility increases with temperature
Exothermic - solubility decreases with temperature

Question 22

Gibbs free energy equation topic 5

Answer 22

Gibs = deltaH - TdeltaS

Question 23

Enthalpy of atomization

Answer 23

Solid atom to gaseous atom

sublimation

Question 24

Bond enthalpy (covalnet bond)

Answer 24

1 mol of bonds broken in gaseous state

M2(g) = 2M(g)

Question 25

Enthalpy of ionization

Answer 25

M(g) = M+ (g) + e-
Gas to ion and electron

Question 26

Enthalpy of electron affinity

Answer 26

X(g) + e- = M-(g)
1 mol of electrons added to 1 mol gaseous atom to make 1 mol of negative gaseous atoms

Question 27

Enthalpy of formation

Answer 27

1 mol substance formed in standard state from elements in standard state

Question 28

Enthalpy of hydration

Answer 28

Forming dilute ion
M+ (g) = M+ (aq)

Question 29

Enthalpy of solution

Answer 29

Mx (s) = M+ (aq) + X- (aq)
1 mol ionic substance dissolved in water to form aqueous solution

Question 30

What do you have to remember when calculating bond enthalpies such as in 2H2O

Answer 30

Multiply bond enthalpies by 2

Question 31

Predict weather Mn2+ or Fe+ is likely to have a more exothermic enthalpy of hydration

Answer 31

Fe2+ because smaller atomic radius so stronger interaction with polar water molecules

Question 32

Why would you have different values using bond enthalpies or enthalpy of formation

Answer 32

Enthalpy of formation values are specific to the compound whereas bond enthalpy averages are from many different compounds

Question 33

Is increasing the temperature of the solution endothermic or exothermic?

Answer 33

Exothermic, releasing energy and heat which increases temp