thermodynamics

Question 1

hess law

Answer 1

enthalpy change for a chemical reaction is the same,regardless of route taken from reactants to products

Question 2

standard enthalpy of formation

Answer 2

enthalpy change when one mole of compound is formed from its elements under standards conditions ,all reactants and products in their standard states

Question 3

standard enthalpy of combustion

Answer 3

enthalpy change when one mole of a compound is completely burned in excess oxygen under standard conditons,all reactants and products in their standard states

Question 4

the standard enthalpy of atomisation

Answer 4

enthalpy change when one gaseous atoms is formed from an element in its standard state

Question 5

mean bond enthalpy

Answer 5

enthalpy change when one mole of gaseous molecules each break a covalent bond to form two free compounds, averaged over a range of compounds

Question 6

more negative lattice formation enthalpy means?in terms of ionic bonds?

Answer 6

stronger ionic bonds

Question 7

what determines the ionic bond strength

Answer 7

smaller ion=stronger ionic bonding
higher charge=stronger bond

Question 8

how do you know when a molecule has covalent character

Answer 8

when the theoretical value of lattice formation is much different to the value of experimental

Question 9

standard enthalpy of hydration

Answer 9

the standard enthalpy change when one mole of gaseous ions is converted into one mole of aqueous ions

Question 10

how would u answer a q comparing strength of ionic bonds

Answer 10

-charge on ions
-radius/size of ions
-attraction between ions
-more exo/endo

Question 11

what is meant by covalent character (example Zn2+ and Se2-)

Answer 11

The Zn2+ ion is quite small with quite a strong +ve charge.
The Se2- ion is large with a diffuse electron cloud.
The two will ionically bond because of the electrostatic attraction.

Question 12

when an ionic solid dissolves in solution, what happens in terms of bonds

Answer 12

-ionic bonds break
-attraction form between ions and water
-delta plus H attracted to negative ion
-delta minus O attracted to positive ion

Question 13

equation for standard enthalpy of hydration for sodium?

Answer 13

Na+(g) + (aq) —–> Na+(aq)

Question 14

equation for standard enthalpy of solution for KCL

Answer 14

KCL(s) + (aq)——–> K+(aq) + Cl-(aq)

Question 15

Gibbs equation?

Answer 15

delta G = delta H - (TdeltaS)

Question 16

gibbs equation in the y=mx+c format

Answer 16

delta G = deltaSxT + deltaH