CH3.6 Enthalpy changes for solids and solutions

Question 1

enthalpy change

Answer 1

a way of measuring the change in energy during any chemical or physical change. We can treat energy and enthalpy as the same thing.

Question 2

principle of conservation of energy

Answer 2

Energy can not be created or destroyed, but may only be converted from one form to another

Question 3

Hess’s law

Answer 3

The energy change of any chemical reaction is the same regardless of the route taken

Question 4

Enthalpy change equation

Answer 4

Enthalpy change = (delta)H(for all products)-(delta)H(for all reactants)

Question 5

exothermic reaction

Answer 5

is one that gives out energy as heat leaving, less chemical eergy in the products that was present in the reactnats

Question 6

endothermic reaction

Answer 6

is one that takes in energy as heat, leaving ore chemical energy in th eproducts thatn was present in the reactants at the start.

Question 7

enthalpy change of reaction

Answer 7

is the change in the chemical energy present in substances during a chemical reaction

Question 8

standard enthalpy change

Answer 8

occurs betwween molar quantities of reactants in thei standard state under standard conditions

Question 9

what are the standard condtions

Answer 9

temperature 298(K) a concentration of 1moldm-3 for solutioins, a pressure of one atmosphere (1atm) for gases

Question 10

standard state

Answer 10

is the physical state of a substance under standard conditions.

Question 11

standard enthalpy change of atomisation

Answer 11

This is the enthalpy change that occurs when one mole o atoms of an element in the gas phase are formed from the element in its standard state under standard conditions

Question 12

standard enthalpy change of atomisation equation example

Answer 12

Na(s) –> Na(g)

Question 13

standard enthalpy change of lattice formation

Answer 13

This is the enthalpy change that occurs when one mole of an ionic compound is formed from ions of the element in the gas phase. It is always exothermic and the more exothermic the more stable the ionic compound is.

Question 14

Standard enthalpy change of lattice formation equation example

Answer 14

Na+(g) + Cl-(g) –> NaCl(s)

Question 15

standard enthalpy of lattice breaking

Answer 15

the energy chagne that occurs when one mole of an ionic compoundis broke up into ions of the elements in the gas phase

Question 16

standard enthalpy change of lattice breaking equations example

Answer 16

NaCl(s) –> Na+(g) + Cl-(g)

Question 17

standard enthalpy change of hydration

Answer 17

This is the enthalpy change that occurs when one mole of an ionic compound in solution is formed from ions of the elements in the gas phase

Question 18

standard enthalpy change of hydration equation example

Answer 18

Na+(g) + Cl-(g) + aq –> NaCl(aq)

Question 19

Electron affinity

Answer 19

This is the enthalpy change that occurs when one mole of gaseous negative ions are formed from gaseous atomsof a substance by gaining an electron

Question 20

Electron affinity equation example

Answer 20

Cl(g) + e- –> Cl-(g)

Question 21

ionisation energy

Answer 21

This is the enthalpy change that occurs when one mole of gaseous positive ions are formed from gaseous atoms, by the substance losing an electron.

Question 22

ionisation energy equation example

Answer 22

Na(g) –> Na+(g) + e-

Question 23

what kind of bond does water create

Answer 23

polar water molecules cause tempory-tempory dipoles with ions

Question 24

standard enthalpy change of solution

Answer 24

This is the enthalpy cahnge that occurs when one mole of substance dissolves completely in a solvent under standard conditions to form a solution

Question 25

standard enthalpy change of solutions equations example

Answer 25

M+X-(s) –> M+(g) + X-(g) –> M+(aq) + X-(aq)

Question 26

enthalpy of lattice breaking, endothermic or exothermic

Answer 26

endothermic

Question 27

enthalpy of lattice hydration, endothermic or exothermic

Answer 27

exothermic

Question 28

How enthalpy of lattice breaking and enthalpy of hydration relate to the soubility of salts

(exothermic)

Answer 28

If the enthalpy of lattiec hydration is greater the the enthalpy of lattice breaking then the salt dissolves, if its the other way around the salt will not usually dissolve. The more exothermic the total of the values the more solouble a salt is likely to be.

Question 29

What will increase the entahlpy of lattice hydration and enthalpy of lattice breaking (2)

Answer 29

increasing the charge on the ions,

decreasing the size of the ions

Question 30

order of the enthalpy changes in a Born-Haber cycle

Answer 30

Enthalpy of formation, Enthalpy of atomisation of gas, Enthalpy of atomisation of metal, Ionisation energy, Electron affinity, Enthalpy of lattice formation.

Question 31

calculation

Enthalpy of lattice formation =

Answer 31

Enthalpy of lattice formation = - electron afffinity - ionisation energy - enthalpy of atomisatio - enthalpy of atomisation + enthalpy of formation

Question 32

what if the enthalpy of formation of a compoundis negative

Answer 32

The energy is given out as the compound is formed its elements, THis tells us that the compound is stbale compared with the elemtns. The more negative the enthaly chagne of formations of a compound the more stable it is.

Question 33

what if the enthalpy change of formation is positive

Answer 33

The compoundus unstable compared with the elemtns that make it up. This does not mean the compound connot exist, but it means that energy is needed to change the elements into the compound.