Thermochemistry/Thermodynamics

Question 1

System v. Surroundings

Answer 1

System is what we’re observing while the surroundings is everything else.

Question 2

Describe the three types of systems.

Answer 2

• Open systems- System exchanges energy ( heat or work) and matter with surroundings.
• Closed Systems- System exchanges energy ( heat or work) but not matter with surroundings.
• Isolated systems- system cannot exchange energy ( heat or work) nor matter with surroundings.

Question 3

Isothermal process

Answer 3

When a change in the system is characterized by constant temperature this changes the equation for the 1st law of thermodynamics to Q=W.

Question 4

Process

Answer 4

When a system undergoes a change

Question 5

Adiabatic process

Answer 5

They system does not exchange heat with the surroundings. Change in the internal energy of a system is equal to the work done by the system.

Question 6

Isobaric process

Answer 6

System contains a constant pressure. Does not change the 1st law of thermodynamics equation.

Question 7

Isovolumetric process

Answer 7

The volume of the system does not change. Because the volume doesn’t change there’s no work done on the object and therefore there’s no area under the PV graph.

Question 8

What’s the equation that represents the change in internal energy of a system?

Answer 8

U = Q - W, where Q is the heat added to the system and W is the work done by the system.

Question 9

Spontaneous v. Nonspontaneous reactions

Answer 9

Spontaneous reactions happens without the input of energy. Nonspontaneous reactions requires input of energy.

Spontaneous reactions doesn’t necessarily mean quick, only catalysts make them quicker.

Question 10

How can we drive nonspontaneous reactions?

Answer 10

We couple them with spontaneous reactions.

Question 11

State function v. Process function

Answer 11

State function describes a system’s equilibrium state. The process function describes how the system moves from one equilibrium state to another.

Question 12

What are the standard conditions?

Answer 12

298K, 1 atm, 1M concentration

Question 13

What does it mean when we say elements are in their standard states?

Answer 13

They’re in their most stable form

Question 14

Phase diagrams

Answer 14

Shows the equilibriums and phase stages at different temperatures and pressures.

Question 15

Vapor pressure

Answer 15

The pressure exerted by gas molecules at the surface of a liquid undergoing evaporation.

Question 15

Evaporation

Answer 15

When liquid molecules gain enough KE to move into the gaseous phase.

Question 15

Condensation

Answer 15

Countering pressure from the atmosphere causes some of the gas molecules to turn back into the liquid phase.

Question 16

Boiling point

Answer 16

The point in which the vapor pressure equals the atmospheric pressure.

Question 17

What’s the transition from a solid to a liquid? Liquid to solid?

Answer 17

Melting, fusion

Solidifying, crystallizing, freezing

Question 18

Sublimation V. Deposition

Answer 18

Sublimation is when a solid transitions directly to a gas. Deposition is when a gas directly into being a solid.

Question 19

Triple point

Answer 19

The point where the 3 phases exist in equilibrium

Question 20

Critical point

Answer 20

When the densities between the liquid and gas phases are equal we cannot distinguish between the 2 phases.

Question 21

Enthalpy

Answer 21

The amount of heat in a system. It’s related to the kinetic energy of the molecules.

Question 22

Zeroth law of thermodynamics

Answer 22

Systems are in thermal equilibrium with each other when their temperatures are the same.

Question 23

What is the unit of heat?

Answer 23

The joule or calories
1 cal = 4.184 j

Question 24

The transfer of heat

Answer 24

Heat is the transfer of energy from the hotter object to the cooler object. Calculated via mcat where m = mass, c = specific heat capacity, t= temperature.

Specific heat is the amount of heat required to raise 1 g of a substance 1 degree celsius.

Question 25

How do we measure the transfer of heat energy?

Answer 25

Via a calorimeter. There are two types: a constant pressure and a constant volume.

Question 26

Describe the points where heat is not changing on a heat curve?

Answer 26

All the heat being added is being used to overcome the equilibrium between those two phases.

Question 27

How do we determine the amount of heat absorbed or released using a heat diagram?

Answer 27

For when heat is changing it’s mcat. When during equilibrium it’s ml where l is latent heat.

to find heat absorbed or released across multiple boundaries you add all the heats.

Question 28

Standard enthalpy of formation

Answer 28

The enthalpy required to produce 1 moles of a compound from elements in their standard states.

Question 29

Standard heat of reaction

Answer 29

Change in enthalpy of a reaction happening under standard conditions.

To find subtract the enthalpy of the products ( multiplied by their coefficients) by the reactants ( multiplied by their coefficients).

Question 30

Hess’s law

Answer 30

The enthalpy of reaction can be found by summing all of the enthalpies of the individual elementary reactions.

Whatever we do to the elementary reactions we do to the corresponding enthalpies, we change them to make them like the overall reaction.

Question 31

Bond dissociation energy

Answer 31

The energy needed to break a covalent bond.

Found by subtracting the enthalpy of the reactants ( bonds broken) by the products (bonds formed).

• Breaking bonds is an endothermic process and forming bonds is a exothermic process.

Question 32

Standard heat of combustion

Answer 32

The enthalpy changes due to a combustion reaction.

Question 33

Second law of thermodynamics

Answer 33

Describes entropy. Everything in the universe moves towards disorder.

• Positive entropy- more disorder.
• Negative entropy- less disorder.

Question 34

How to calculate change in entropy?

Answer 34

We subtract the entropies of the products ( multiplied by the coefficients) by the reactants ( also multiplied by the coefficients).

Question 35

Gibb’s free energy

Answer 35

Energy available to do useful work.
- Exergonic - spontaneous, negative value.
- Endergonic- nonspontaneous, positive value.

Question 36

Connection between movement of chemical reaction and free energy.

Answer 36

Exergonic- moving towards equilibrium, spontaneous reaction.

Endergonic- moving away from equilibrium, nonspontaneous reaction.

Question 37

Standard free energy of formation

Answer 37

Free energy change associated with the formation of 1 mole of a compound from elements in their standard states.

Question 38

Standard state elements has how much energy?

Answer 38

Elements that’s in their standard states has a free energy change of zero.