Energetics

Question 1

What is an Endothermic reaction?

Answer 1

A reaction which absorbs heat (+ve)

Breaking of bonds

Question 2

What is an exothermic reaction?

Answer 2

A reaction which produces heat (-ve)

Formation of bonds

Question 3

In an enthalpy diagram what us stable and non stable state and their positions?

Answer 3

Stable- energy released-lower position

Unstable-energy gained-higher position

Question 4

What is the specific heat capacity of water?

Answer 4

4.18kj/k kg

Question 5

What is Hess’s Law?

Answer 5

The enthalpy change of a reaction depends only on the initial and final states of the of the reaction-independent of the route

Question 6

Combustion enthalpy equation?

Answer 6

\ / reactants-products

Question 7

Formation enthalpy equation?

Answer 7

\ / up- products - reactants

Question 8

What is average bond enthalpy?

Answer 8

The mean of the enthalpy required to break a particular covalent bond in a range of molecules
-APPROXIMATE VALUES

Question 9

What is the equation for average bond enthalpy

Answer 9

(Enthalpy of bonds broken)-(Enthalpy of bonds formed)

Question 10

What is standard state?

Answer 10

101kPa, 298K,

1atm 25Celcius

Question 11

What is standard enthalpy formation?

Answer 11

The enthalpy change when 1 mole of a substance is made from its elements in their standard state
Na + Cl—NaCl

Question 12

What is Standard Enthalpy of Combustion?

Answer 12

The enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions

Question 13

What is Ionization Enthalpy?

Answer 13

The enthalpy change when 1 mole of gaseous 1+ ions are formed from 1 mol of gaseous atoms
Na(g)–Na+(g) + e-

Question 14

What is electron affinity?

Answer 14

The enthalpy change when 1 mol of gaseous atoms each gain 1 electron
Cl + e—Cl-(g)

Question 15

What is Bond Dissociation Enthalpy?

Answer 15

The breaking of a covalent bond in a gaseous molecule to form two gaseous free radicals
Cl2(g)—2Cl
CH4(g)–CH3(g) + H

Question 16

What is Enthalpy of Atomization?

Answer 16

The Enthalpy change when 1 mole of atoms in gaseous state is formed from the element in its standard state
1/2Cl2(g)–Cl(g)
Na(s)–Na(g)

Question 17

What is Lattice Enthalpy?

Answer 17

The separation of 1 mol of a solid ionic lattice into its constituent gaseous ions(dissociation)
NaCl(s)—Na+(g) + Cl-(g)
(Formation) (-ve) Na+(g) + Cl(g)–NaCl(s)

Question 18

What is the equation for the enthalpy of formation

Answer 18

The sum of all steps = enthalpy of formation

Question 19

What does lattice Enthalpy change with?

Answer 19

1. Size of ions-as size getw bigger lattice enthalpy attraction gets greater because more shielding, easier to bond
2. Charge on ions-the bigger the ion the bigger the lattice enthalpy

Question 20

What is Entropy?

Answer 20

Degree of disorder

Question 21

What factors increase disorder in a system? (4things)

Answer 21

1. Increase number of particles
2. Mixing of particles
3. Change of state to greater distance between particles
4. Increase particle movement

Question 22

Equation for Entropy?

Answer 22

S(products)-S(reactants)

Question 23

What is meant by Gibbs Free Energy?

Answer 23

A measure of total entropy of the universe.

Question 24

Gibbs equation?

Answer 24

G=H-TAS/1000

Question 25

Entropy increases in what kind of reactions?

Answer 25

Exothermic, relaeaee energy, increase entropy

Question 26

Retionship os entropy with Gibbs

Answer 26

Positive entropy= negative gibbs= spontaneous

Negative entropy=positive gibbs=not spontaneous

Question 27

Enthalpy of Formation

Answer 27

When a compound is made from its constituent elements in their standard states