Module #13: Thermodynamics

Question 1

Define Enthalpy (H).

Answer 1

The energy stored in a substance.

Question 2

What is Change in Enthalpy (ΔH)?

Answer 2

The energy change that accompanies a chemical reaction. (KJ - kiloJoules) (kcal - kilocalories)

Question 3

What is 1 calorie = to?

Answer 3

1 calorie = 4.184 Joules

Question 4

ΔH is ___ for endothermic reactions

Answer 4

ΔH is positive for endothermic reactions

Question 5

ΔH is ____ for exothermic reactions.

Answer 5

ΔH is negative for exothermic reactions.

Question 6

What is the energy equation?

Answer 6

q = mcΔT

Question 7

Define Bond Energy.

Answer 7

The strength of a chemical bond.

Question 8

What is a State Function?

Answer 8

Any quantity that depends solely on the the final destination, not on the way you get to that destination.

Question 9

Define Standard Conditions.

Answer 9

Room temperature (25 degrees) and pressure of 1.00 atm

Question 10

What is the standard enthalpies of formation?

Answer 10

ΔH~f for molecules under standard conditions.

Question 11

What is the formula for ΔH?

Answer 11

ΔH = (Energy required to break bonds) - (Energy released when bonds form)

Question 12

What is Hess’s Law?

Answer 12

Enthalpy is a state function and is therefore independent of path.

Question 13

What is the Enthalpy of formation (ΔHf)

Answer 13

The ΔH of a formation reaction

Question 14

Define Activation Energy.

Answer 14

The energy necessary to start a chemical reaction

Question 15

Define Entropy (S).

Answer 15

A measure of the disorder that exists in any system { ΔS~universe >= 0 }
Energy Unit / Moles * Kelvin

Question 16

What is The Second Law of Thermodynamics?

Answer 16

The entropy of the universe must always either increase or remain the same. It can never decrease.

Question 17

What is the formula for ΔHf^o (enthalpy of a reaction)

Answer 17

ΔHf^o = [Summation] ΔHf^o (products) - [summation] ΔHf^o (reactants)

Question 18

What is the standard enthalpy of formation of an element in its elemental form?

Answer 18

The standard enthalpy of formation of an element in its elemental form is zero?

Question 19

What is the intermediate state, the part of the reaction that needs energy to start it off, analogous to?

Answer 19

The intermediate state is analogous to activated complex.

Question 20

What is the order of entropy in substance states?

Answer 20

The solid state has the least amount of entropy associated with it. The entropy of the liquid state is higher, and the entropy of the gaseous state is the higher of all.

Question 21

What does entropy increase accordingly with?

Answer 21

The entropy of a system increases with increasing temperature and with increasing mass.

Question 22

What is the entropy (ΔS^o) formula?

Answer 22

ΔS^o = ∑ S^o (products) - ∑ S^o (reactants)

Question 23

What has an absolute entropy?

Answer 23

All substances, even elements, have an absolute entropy.

Question 24

Define the Gibbs Free Energy (ΔG) formula.

Answer 24

A very simple formula that relates ΔS and ΔH to find whether a chemical reaction is consistent with the Second Law. (for temp. Of 298 K)

Question 25

What is the Gibbs Free Energy (ΔG) formula?

Answer 25

ΔG = ΔH - T * ΔS

—> ΔG = Gibbs Free Energy, if reaction is consisted with the Second Law of Thermo.
—> ΔH = Energy released (kJ)
—> T    = Temperature of the surroundings, Kelvin
—> ΔS = The disorder J / moles * K

Question 26

How do you tell if a reaction conforms to the second law of thermodynamics?

Answer 26

If the Gibbs Free Energy formula results in a positive number, it is NOT SPONTANEOUS, whereas, if it’s negative, it IS SPONTANEOUS.

Question 27

What is the Gibbs Free Energy Formula for reactions with temperatures of 298 K?

Answer 27

ΔGo = ∑ ΔGf^o (products) - ∑ ΔGf^o (reactants)