Chemistry Video 11

Question 1

Energy

Answer 1

Capacity to do work. Displacement of an object. Chemical reactions require energy to occur. Measured in Joules (J)

Question 2

Kinetic energy

Answer 2

Energy of motion

Question 3

Potential energy

Answer 3

Energy of location

Question 4

First law of thermodynamics

Answer 4

Conservation of energy. Energy is not created nor destroyed, it only changes forms.

delta U = q + w

q = heat 
w = work
U = internal energy; sum of the energies present in the system

Internal energy increases if heat is absorbed or if work is done on the system by the surroundings

Internal energy decreases if heat is releases or work is done by the system

+ q = heat flows in
- q = heat flow out
+ w = work done on the system
- w = work done by the system

Question 5

Expansion work

Answer 5

A type of work. Pressure-volume work.

Occurs when a system pushes against the pressure of its surroundings. i.e. internal combustion engines

Question 6

State function

Answer 6

Depends on current state of system and not how the system got there.

i.e. internal energy.

Question 7

Not state function

Answer 7

Depends on how the system got there.

i.e. heat and work

Question 8

delta Enthalpy

Answer 8

delta H; The sum of a system’s internal energy and the product of its pressure and volume

delta H = delta U + (P)*(delta V)

Internal energy, pressures and volume are all state functions. Therefore, enthalpy is also a state function.

Question 9

(P)*(delta V)

Answer 9

Represents the expansion work done by the system.

(P)*(delta V) = -w

Question 10

Change in enthalpy is also equal to…

Answer 10

delta H = q

change in enthalpy is the same as heat exchanged when a system remains at constant pressure

delta H = (delta H of reactants) - (delta H of products)

Question 11

Bonds breaking vs forming

Answer 11

Bond breaking needs energy. Bond forming releases energy.

Question 12

Negative delta H

Answer 12

Exothermic, energy released

Question 13

Positive delta H

Answer 13

Endothermic, energy absorbed

Question 14

Stoichiometric value of enthalpy

Answer 14

Specific to the molar quantities listed in an equation.

If the coefficients in an equation double, then the change in enthalpy also needs to double

If the direction of the reaction is reversed, then the sign on the change in enthalpy must reverse

Question 15

Dynamic equilibrium

Answer 15

Changing from 2 phases at the same rate. i.e. going from water to liquid and from liquid to water at the same rate

Question 16

Vapour pressure

Answer 16

The pressure exerted by dynamic equilibrium between liquid and gas. Increases with increasing temperature

Question 17

Boiling point

Answer 17

When the vapour pressure is equal to the surrounding pressure of a liquid

Question 18

Vaporization

Answer 18

Endothermic process. Liquid to gas. Heat energy needed.

Question 19

Enthalpy of vaporization

Answer 19

The energy associated with the vaporization process.

Enthalpy of vaporization of water at room temperature is 40.65 kJ/mol.

Question 20

Condensation

Answer 20

Exothermic. Gas to liquid. Heat energy released.

40.65 kJ of energy released per mole of water.

Question 21

Heat added to solid

Answer 21

As heat is added to solid, its temperature increases.

When the melting point is reached, more heat will NOT go towards raising the temperature of the solid. The heat will disrupt the lattice structure of the solid. The temperature remains constant through the process of melting.

Once completed melted, additional heat will continue to raise the temperature of the substance

Question 22

Melting point/freezing point.

Answer 22

Temperature at which there is equilibrium between solid and liquid phases. They are both the same temperature. Freezing and melting occurs at equal rates.

Question 23

Enthalpy of fusion

Answer 23

energy needed to melt a solid.

Weak interactions in solid result in low melting point and smaller enthalpy of fusion.

Enthalpy of fusion is 6.02 kJ/mol for water.

Question 24

Freezing

Answer 24

Exothermic. Liquid to solid. Heat energy released

Question 25

Melting

Answer 25

Endothermic. Solid to liquid. Heat energy needed

Question 26

Sublimation

Answer 26

Solid to gas. Endothermic. Heat energy needed

Enthalpy of sublimation for carbon dioxide is +26 kJ/mol

Question 27

Deposition

Answer 27

Gas to solid. Exothermic. Heat energy released.

Enthalpy of deposition for carbon dioxide is -26 kJ/mol

Question 28

Calorie

Answer 28

cal, amount of energy needed to raise the temperature of one gram of water by 1 degrees Celsius

Question 29

Joule

Answer 29

SI unit for energy, the amount of energy utilized when a 1 N force moves an object a distance of 1 meter

1 Joule = 1 kg m^2/s^2
1 cal = 4.184 J

Question 30

Heat capacity

Answer 30

Extensive property that depends on amount of substance

Energy needed to raise the temperature of an object by 1 degrees Celsius

OR

Energy released when the temperature of an object is reduced by 1 degrees Celsius

C = q / delta T

q = heat
C = heat capacity in J/degrees Celsius units

Question 31

Specific heat capacity AKA specific heat

Answer 31

Intensive property that does not depend on amount of substance.

Energy required to raise the temperature of 1 gram of a substance by 1 degrees Celsius

q = mcdelta T

c units is J/g degrees C

Question 32

Calorimeter

Answer 32

Calibrated device that measures heat transferred (and associated values like temperature)

i.e. coffee cup calorimeter with styrofoam

Question 33

Heating and cooling curves

Answer 33

Shows ice, water and steam as having a non-zero slope because temperature is changing as energy is added.

Ice & water and water & steam are flat horizontal lines because temperature is not changing as energy is added.

Question 34

Hess’ Law

Answer 34

Change in enthalpy for a reaction is a state function. Can write out a reaction as the sum of several other equations with known enthalpy change. The sum of the enthalpy change of the several equations is equal to the unknown enthalpy change of the full reaction

Question 35

Enthalpy of formation

Answer 35

Energy associated with the formation of one mole of a compound from its respective elements in their most stable states and under standard conditions.

Symbol is delta H subscript f superscript degrees

Standard state elements have 0 enthalpy of formation

Question 36

Change in enthalpy equation with enthalpies of formation

Answer 36

Change in enthalpy = (sum of enthalpies of formation of products) - (sum of enthalpies of formation of reactants)

Question 37

Adiabatic process

Answer 37

Occurs without any transfer of heat or mass between system and surroundings.

Question 38

Isobaric process

Answer 38

Pressure is constant

Question 39

Isochoric process

Answer 39

Volume is constant

Question 40

Isothermal process

Answer 40

Temperature is constant