Energies

Question 1

Exothermic reaction

Answer 1

One that releases heat to the surroundings as a result of forming products with stronger bonds than reactants. These have a negative enthalpy value

Question 2

Endothermic reaction

Answer 2

One that absorbs heat from the surroundings as a result of forming products with weaker bonds than reactants. These have a positive enthalpy value

Question 3

Standard enthalpy change of reaction

Answer 3

change is the heat transferred during a reaction carried out under certain conditions.
Pressure 100kPa
Temperature 278k
all substances in their pure and standard state

Question 4

Average bond enthalpy

Answer 4

The required energy to break a mole of covalent bonds in the reactant, all reactants and products being in gas form.

Question 5

Standard state

Answer 5

An element or compound in its most stable state under specified conditions

Question 6

Standard enthalpy change of formation

Answer 6

The enthalpy change on the formation of one mole of a compound from its elements in their standard states under certain conditions

Question 7

Standard enthalpy change of combustion

Answer 7

The enthalpy change on the complete combustion of one mole of a compound in its standard state

Question 8

Lattice Enthalpy

Answer 8

Enthalpy change which occurs on the formation of one mole of ionic compound from its isolated ions in their gas state. An exothermic reaction

Question 9

Standard Temperature and pressure

Answer 9

273K and 100kPa

Question 10

free energy change or (delta G) gibbs free energy

Answer 10

Delta G is related to the entropy change of the universe and can be defined using the equation:
DeltaG = DeltaH-T delta S
for a reaction to be spontaneous, Delta G for the reaction must be negative; delta G is the standard free energy charge

Question 11

HESS’S LAW

Answer 11

Enthalpy change accompanying a chemical reaction is independent of the pathway between the initial and final states.

Question 12

Spontaneous reaction

Answer 12

A reaction that occurs without any outside influence. E.g no input energy and delta G is negative

Question 13

Standard Enthalpy change of Atomisation (delta HAT)

Answer 13

the enthalpy change when one mole of gaseous atom is formed from an element

Question 14

Standard Enthalpy change of Combustion (delta HC)

Answer 14

enthalpy change (heat is given out) When one mole of a substance is completely burnt in oxygen under standard conditions

Question 15

Standard Enthalpy change of Formation (Delta HF)

Answer 15

change when one mole of the substance is formed from its elements in their standard states under standard conditions; Delta Hf for any element in its standard state is zero

Question 16

Standard Enthalpy change of Hydration (deltaH HYD)

Answer 16

Change when one mole of gaseous ions are surrounded by water molecules to form an ‘infinitely dilute solution” under standard conditions: DeltaH HYD

Question 17

Standard Enthalpy change of Neutralisation (deltaHN)

Answer 17

change when one mole of H20 molecules are formed when an acid (H+) reacts with an akali (OH-) under standard condtions.

Question 18

Standard state

Answer 18

Pure substance at 100 kPa and a specified temperature (assume 298k if one is not given) It is often used to refer the state in which a substance exists under standard conditions