Enthalpy Changes for solids and solutions (3.6)

Question 1

Hess’s Law

Answer 1

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

Question 2

Enthalpy of formation equation

Answer 2

Enthalpy change=ΔH f(products)-ΔH f(reactants)

Question 3

Standard Conditions

Answer 3

298K, 1moldm-3, 101kPa,

Question 4

Standard State

Answer 4

The physical state of a substance under standard conditions

Question 5

Standard Enthalpy of reaction

Answer 5

The enthalpy change that occurs in a reaction between molar quantities of reactants in their standard state under standard conditions.

Question 6

Standard Enthalpy change of atomisation

Answer 6

Enthalpy change that occurs when one mole of atoms of an element in the gas phase are formed from in the element in it standard state under standard conditions

Question 7

Standard Enthalpy Change of lattice formation

Answer 7

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

Question 8

Standard enthalpy change of hydration

Answer 8

Enthalpy change when one mole of an ionic compound in solution is formed from ions of the elements in the gas phase

Question 9

Electron Affinity

Answer 9

The enthalpy change when one mole of gaseous negative ions are formed from gaseous atoms of a substance by gaining an electron.

Question 10

Ionisation Energy

Answer 10

The enthalpy change when one mole of gaseous positive ions are formed from gaseous atoms of a substance by losing an electron.

Question 11

Enthalpy change of combustion

Answer 11

The enthalpy change which occurs when one mole of the compound is burned completely in oxygen under standard conditions, and with everything in its standard state.

Question 12

Enthalpy Change of formation

Answer 12

The enthalpy change when one mole of a compound is formed from its constituent elements in their standard states under standard conditions.

Question 13

What are ionic substances held together by?

Answer 13

Electrostatic forces

Question 14

Enthalpy Change of Solution

Answer 14

The enthalpy change that occurs when one mole of substance dissolves completely in a solvent under standard conditions to form a solution.

Question 15

Is lattice breaking endothermic or exothermic?

Answer 15

Endothermic

Question 16

Is lattice of hydration endo/exothermic?

Answer 16

Exothermic

Question 17

Factors Affecting enthalpy of LB and EoH

Answer 17

Both increased by increasing charge on the ions

Both increased by decreasing size of ions

Question 18

Formula for Standard enthalpy of Solution

Answer 18

Standard enthalpy of hydration+enthalpy of lattice breaking

Question 19

How do you know if a substance will dissolve

Answer 19

If EoH is greater than LB, salt dissolves

If EoH is less than LB, salt doesn’t dissolve

Question 20

Stability of Compounds

Answer 20

More negative the enthalpy change of formation, the more stable it is