Exam 1 Study Material: Thermodynamics

Question 1

What is energy a measure of and what are the different types of energy?

Answer 1

Energy is a measure of a system’s ability to do stuff. There are two types: potential and kinetic. Potential energy is associated with position and composition whereas kinetic energy is a measure of motion

Question 2

What is Coulomb’s law dependent on?

Answer 2

Coulombs law is dependent on potential energy —> r is distance between particles

Question 3

Which phase of matter has the highest KE has the highest KE and which variable (T, P, V, n) is most closely related to KE?

Answer 3

Gases have the highest KE and Temperature is most closely related to KE

Question 4

At phase transitons which has the highest KE, liquid or gaseous water and why?

Answer 4

At the phase transition, both phases are at the same TEMPERATURE so they have the same KE

Question 5

Which phase of water, liquid or gas has the smallest PE and why?

Answer 5

Liquid water has the smallest amount of PE because particles are closer leading to stability

Question 6

What are the two ways that a system gains and loses energy?

Answer 6

A system loses or gains energy through heat (δq) and work (δw). δq represents a change in heat, representing the amount of thermal energy added to or removed from a system. δw is mechanical energy done by or on the system.

Question 7

What does it mean when δq is negative? positive?

Answer 7

δq is negative when heat is lost by the system and absorbed by the surroundings. δq is positive when heat is absorbed by the system and lost by the surroundings.

Question 8

What does it mean when δw is negative? positive?

Answer 8

δw is negative when a gas expands, so the system does work on the surroundings. δw is positive when a gas is compressed, so the surroundings does work on the system.

Question 9

What type of motion is δw and δq?

Answer 9

δq is random motion while δw is ordered motion

Question 10

What equation describes δq and units?

Answer 10

δq= moles x resistance to heating x temperature change (=molJ/molKK=J)

Question 11

How do we define a system and surroundings?

Answer 11

The system is the component that undergoes an energy change; and acts. The surroundings is the component that responds to that action and enables the system to undergo that change.

Question 12

What is kinetic molecular theory?

Answer 12

KMT explains how gas particles move and interact to give us the macroscopic properties we observe, like pressure and temperature, using ideal gases as the model.

Question 13

Can we know the KE of each gas particle?

Answer 13

No! We can only know the average molar KE because it is not practical to measure the instantaneous speed of all gas particles

Question 14

What is the equation for urms and what does it tell us?

Answer 14

Urms=sqrt(3RT/Mw) with R equaling 8.314 J/molK. It tells us that light gases at high temperatures move fastest

Question 15

What does the R value mean in the urms equation?

Answer 15

R is the amount of work done by 1 mol of an deal gas upon changing its T by 1 K at fixed P

Question 16

At constant P, what property changes with T?

Answer 16

Volume must increase with temperature.

Question 17

On a Boltzmann graph, where can you find Urms and why?

Answer 17

Urms will be found to the right of the speed where the highest number of atoms are traveling because there are more atoms at a higher speeds than lower speeds.

Question 18

How does the Urms graph of a gas moving fast look? moving slowly?

Answer 18

A graph that displays a fast-moving gas will be broad and shifted to the right. A slow-moving gas will be shifted left and will appear narrow.

Question 19

What does temperature tell us?

Answer 19

T tells us how fast particles are moving

Question 20

At constant volume, what is the work response from a gas that absorbs heat?

Answer 20

δq=+ and δw=0 since work is constant

Question 21

What is the heat capacity of an ideal gas when volume is constant?

Answer 21

When volume is constant, Cv= 3/2R. That number represents an ideal gas’s resistance to a heat change at constant volume

Question 22

How does the heat capacity at constant volume change for a real gas compared to an ideal gas?

Answer 22

Real gases have more forms of motion which means that they have a greater amount of ways to store their energy leading to a great Cv/ resistance to a heat change

Question 23

What does heat and work together sum up to?

Answer 23

Together, heat and work sum up to the amount of internal energy (ΔE) of a system. ΔE=δq+δw

Question 24

What is the first law of thermodynamics?

Answer 24

Heat can neither be created nor destroyed. The TOTAL energy of the universe is constant —> conservation of energy

Question 25

What type of functions are heat and work? Internal energy?

Answer 25

Heat and work are path functions where as internal energy is a state function.

Question 26

What is the difference between a path and state function?

Answer 26

A path function involves physical quantities that depend on the path taken from the initial to the final state. A state function are physical quantity that is independent of the path taken from the initial to the final state.

Question 27

What does Cv correspond to for an ideal gas?

Answer 27

Cv= 3/2R comes from gas KEavg changing

Question 28

Why is Cp greater than Cv?

Answer 28

It requires more energy to change the temperature when the system is able to do work, thus, the gas has a greater resistance to a temperature change

Question 29

What is the value of Cp?

Answer 29

Cp= 5/2R for an ideal gas

Question 30

What is a constant volume calorimetry and how does it work?

Answer 30

Constant volume calorimetry (measurement of heat change) is a measure of ΔE through measure δq because at constant volume, work is not able to done

Question 31

What leads to a greater Cv?

Answer 31

Cv becomes greater as we introduce more ways to store thermal energy

Question 32

What is Cv related to? Which phases of matter tend to have higher heat capacities and why?

Answer 32

Cv is related to the ways a substance stores its energy through motion or IMFs. Generally, liquids>solid>real gases> ideal gases. Since liquids have both IMF and many ways to store their energy, they tend to have the greatest heat capacities

Question 33

How does heat resistance relate to bonds?

Answer 33

In bonds with similar structures, as you increase the number of bonds, you increase the heat capacity

Question 34

Describe the energetic interaction of a a hot piece of metal is dropped into a cold water

Answer 34

The metal will release heat that the water absorbs . Because of the first law of thermodynamics, -δqmetal=δqwater

Question 35

When a hot piece of metal is dropped into cold water, at what point will heat stop being transferred?

Answer 35

Heat transfer will stop when both bodies are at the same temperature—>(thermal equilibrium)

Question 36

What is one way that we can calculate ΔE at constant V?

Answer 36

We can calculate ΔE by directly measuring ΔT through bomb calorimetry

Question 37

How does bomb calorimetry work?

Answer 37

Bomb calorimetry involves placing a sample in a sealed container (the bomb), igniting it to undergo combustion, and measuring the resulting temperature change in water surrounding the bomb. By calculating this heat change and considering the heat capacity of the calorimeter, scientists can determine the heat of combustion for the tested substance, providing insights into its energy content.

Question 38

What is defined as the system and the surroundings for bomb calorimetry?

Answer 38

The system is the bomb contents —> reaction and the surroundings are the bomb walls and water

Question 39

Why do reactions release heat?

Answer 39

Reactions release heat in the form of potential energy because the bonds of the product are stronger than reactants

Question 40

Under what conditions do most chemical reactions take place?

Answer 40

Most chemical reactions take place under constant pressure, rather than constant volume

Question 41

What type of function does q become under constant pressure?

Answer 41

Under constant pressure, δq becomes a state function —>ΔH

Question 42

How is ΔH defined?

Answer 42

ΔH is the heat change associated with a chemical/physical process at constant pressure

Question 43

How are ΔH and ΔE similar?

Answer 43

Both ΔH and ΔE account for chemical bond energy, IMF energy, and energy of motion. They are both state functions that describe a heat change

Question 44

What differentiates ΔH from ΔE?

Answer 44

ΔH accounts for the energy of interaction with the environment, so it considers the fact that some heat is dissipated upon expansion

Question 45

What equation describes ΔH and explain how does it work?

Answer 45

ΔH= ΔH+PΔV. This equation has another PΔV that aims to account for the energy loss due to expansion

Question 46

What are two scenarios in which ΔH and ΔE differ?

Answer 46

Production or loss of a gas in a chemical reaction leads to ΔH<ΔE.>ΔE</ΔE.>

Question 47

What do we assume when calculating δw in chemical reactions?

Answer 47

Gas production is the only source of ΔV

Question 48

When are ΔH and ΔE equal to each other?

Answer 48

When the reaction does not involve gases, they are equal

Question 49

What must change with volume when calculating for δq at constant pressure?

Answer 49

At constant pressure, we assume the number of moles changes—-> δq=-PextΔV=-RTΔn

Question 50

What is coffee cup calorimetry and how can we tell when work is done?

Answer 50

Coffee cup calorimetry includes an insulated system where an aqueous phase reaction serves as the system and the water is the surroundings. Ccal=4.184. work is done through displacement of surrounding molecules

Question 51

If two moles of a reaction occur, how does ΔH change?

Answer 51

Since ΔH is per mole of reaction, when the moles are doubled, ΔH value is also doubled

Question 52

What happens to ΔH when a reaction goes the reverse way?

Answer 52

The magnitude of ΔH stays the same, however, the sign changes

Question 53

What is Hess’s Law?

Answer 53

Hess’s law tell us that if a reaction is carried out over multiple steps, ΔH for the nET reaction equals the sum of ΔH for each step.

Question 54

What does Hess’s law use to its advantage?

Answer 54

Hess’s law uses the first law of thermodynamics and ΔH being a state function

Question 55

How can we predict whether a reaction will be endothermic or exothermic?

Answer 55

Atoms bond to gain stability so if the products are more stable than the reactants, the reaction will be exothermic

Question 56

What is Bond Dissociate Energy?

Answer 56

BDE is the energy required to split a chemical bond in half

Question 57

What is the sign of ΔH when a reaction is endo vs exothermic?

Answer 57

ΔH is + when the reaction is endothermic and bonds are broke ΔH is - when a reaction is exothermic and bonds are formed

Question 58

What can we use to predict the energetic driving force of a reaction?

Answer 58

We can use bond dissociation energy and hess’s law

Question 59

What is the relationship between BDE, Bond order, and Bond length?

Answer 59

As Bond order increases, BDE increases, and bond length decreases

Question 60

Which type of bonds are most stable?

Answer 60

σ are the most stable type of bond

Question 61

How does BDE change as the number of bonds go up?

Answer 61

BDE increases as the number of bonds go up due to the stability gained when atoms bond together

Question 62

How can we solve for ΔHrxn?

Answer 62

ΔH= ΣΔHbonds broken - ΣΔHbonds formed