mod 4

Question 1

what is enthalpy of dissolution?

Answer 1

when an ionic compound dissolves in water, its positive and negative ions dissociate from each other and are surrounded by the oppositely charged poles of water molecules

Question 2

what is bond energy?

Answer 2

refers to the energy required to break a specific covalent bond so that individual atoms exist in gaseous form

Question 3

what does a high bond energy tell you?

Answer 3

is an indicator of a strong covalent bond

Question 4

what is standard enthalpy formation?

Answer 4

the standard enthalpy formation refers to the enthalpy change that occurs when 1 mole of a compound is formed in its element

Question 5

what is Hess’ Law?

Answer 5

Hess’ Law (of conservation of heat summation) states that the enthalpy change for an overall reaction is equal to the sum of the enthalpy changes for each step in the reaction

Question 6

what is a system?

Answer 6

the universe can be divided into small parts for study, which is referred to as a system

Question 7

what is an open system?

Answer 7

exchanges matter and energy with its surroundings

Question 8

what is a closed system?

Answer 8

• matter is not exchanged
• energy is the same

Question 9

what is an isolated system?

Answer 9

matter that isn’t exchanged

Question 10

what is the 1st law of thermodynamics?

Answer 10

the total energy in the universe is constant; it cannot be created nor destroyed but it can be transformed or transferred to or from its surroundings

Question 11

what is the formula for the 1st law of thermodynamics?

Answer 11

∆Euniv = ∆Esys + ∆Esurr = 0

Question 12

what is the formula or energy in a system?

Answer 12

energy in a system = kinetic energy (KE) + potential energy (PE)

Question 13

what is enthalpy?

Answer 13

enthalpy (H) is the energy of a system plus the product of pressure and volume

Question 14

what is the enthalpy formula?

Answer 14

H = Esys + PV

Question 15

what is entropy?

Answer 15

entropy is a measure of a system’s thermal energy that is not available for useful work

Question 16

in a system when is there high entropy vs low?

Answer 16

• high entropy is associated with greater disorder or randomness in a system; the more arrangements, the more entropy
• low entropy occurs when there are fewer arrangements or less randomness in a system

Question 17

what is the 2nd law of thermodynamics?

Answer 17

the entropy of the universe is decreasing

Question 18

what is the formula for the 2nd law of thermodynamics?

Answer 18

∆Ssys + ∆Ssurr = ∆Suniverse > 0

Question 19

when does a chemical process occur spontaneously?

Answer 19

a chemical process occurs spontaneously if it increases the entropy of the universe

Question 20

what is standard entropy?

Answer 20

it is the entropy of a chemical substance at standard conditions

Question 21

what is Gibbs Free Energy (∆G)?

Answer 21

it is a concept created to determine if a chemical reaction is spontaneous (or favoured in the forward direction)

Question 22

what is the formula for gibbs free energy?

Answer 22

ΔG° = ΔH° - TΔS°

Question 23

when is the reaction spontaneous?

Answer 23

when ΔH° is -ve and S° is +ve so ΔG < 0

Question 24

when is a reaction not spontaneous?

Answer 24

when ΔH° is +ve and S° is -ve so ΔG > 0

Question 25

when the ΔG is = 0?

Answer 25

ΔG is equilbrium