17.1- ENTHALPY CHANGE

Question 1

What is the standard molar enthalpy of formation ΔfH⦵?

Answer 1

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

Question 2

What is the standard molar enthalpy change of combustion ΔcH⦵?

Answer 2

enthalpy change when one mole of substance completely burnt in oxygen

Question 3

What is the standard enthalpy of atomisation? ΔatH⦵

Answer 3

enthalpy change which accompanies the formation of one mole of gaseous atoms from element in its standard state under standard conditions

Question 4

What is the first ionisation energy ΔiH⦵?

Answer 4

standard enthalpy change when one mole of gaseous atoms converted into a mole of gaseous ions each with a single positive charge

Question 5

What does the second ionisation energy refer to?

Answer 5

loss of a mole of electrons from a mole of singly positively charged ions

Question 6

What is the first electron affinity ΔeaH⦵?

Answer 6

standard enthalpy change when one mole of gaseous atoms is converted to a mole of gaseous ions, each with a single negative charge

Question 7

What is the second electron affinity ΔeaH⦵?

Answer 7

enthalpy change when a mole of electrons is added to a mole of gaseous ions each with a single negative charge to form ions each with two negative charges

Question 8

What is the lattice enthalpy of formation ΔlH⦵?

Answer 8

standard enthalpy change when one mole of solid ionic compounds is formed from its gaseous ions

Question 9

Wheat happens when a lattice forms and what is the ΔH⦵ like?

Answer 9

new bonds formed, resulting in energy being given out, so ΔH⦵ always negative for this process

Question 10

What is the lattice enthalpy of dissociation?

Answer 10

standard enthalpy change when one mole of solid ionic compounds dissociated into its gaseous ions

Question 11

Can lattice enthalpies be measured directly?

Answer 11

no

Question 12

What is done as lattice enthalpies cannot be measured directly?

Answer 12

they’re calculated

Question 13

What is the enthalpy of hydration ΔhydH⦵?

Answer 13

standard enthalpy change when water molecules surround one mole of gaseous ions

Question 14

What is the enthalpy if solution ΔsolH⦵?

Answer 14

standard enthalpy change when one mole of solute dissolves completely in sufficient solvent to form a solution in which the molecules or ions are far enough apart not to interact with each other

Question 15

What is the mean bond enthalpy?

Answer 15

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

Question 16

Where are electrons transferred from to in a simple model of ionic bonding?

Answer 16

electrons transferred from metal atoms to non-metal atoms

Question 17

What sort of ions are formed in ionic bonding?

Answer 17

positively charger metal ions and negatively charged non-metal ions that all have stable outer shlel of electrons

Question 18

How do the positively and negatively charged ions arrange themselves in ionic bonding?

Answer 18

arrange themselves into a lattice so that ions of opposite charge next to one another

Question 19

What happens if positively charged ions come together with negatively charged ions?

Answer 19

form solid lattice + energy given out due to attraction between oppositely charged ions- called lattice formation enthalpy ΔlH⦵

Question 20

What does Hess’s law tell us about total energy change?

Answer 20

total energy change for chemical reaction same whatever route taken, provided initial and final conditions are the same