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Chemistry sem 1 > First Law of thermodynamics > Flashcards

First Law of thermodynamics Flashcards

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1
Q

What are the surroundings

A

anything outside of the system

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2
Q

what confines the system

A

the system boundary

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3
Q

what is an isothermal change

A

when the system is closed which means the temp of the surroundings impacts the temp of the system
the wall is diathermal
exchanging heat

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4
Q

what is an adiabatic change

A

when there is no temp change in the closed system due to the surroundings
the wall is adiabatic

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5
Q

what is a thermodynamic system

A

it is part of the physical universe with a specified boundary for observation

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6
Q

What is the first law of thermodynamics

A

the law relates the internal energy (U) of a system to the amount of heat added to the system and the amount of work done on the system

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7
Q

What is work done

A

work is done when a force is applied to an object and that causes that object to move a distance

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8
Q

what is an open system

A

if there can be matter and heat exchanged with the surroundings like a beaker without a bung or a human body

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9
Q

what is a closed system

A

if heat can still be exchanged but matter cannot like a beaker with a bung or a light bulb

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10
Q

what is an isolated system

A

neither heat nor matter can be exchanged, like a perfect thermal flask or bomb calorimeter

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11
Q

what is the equation for work done

A

deltaU=q + w

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12
Q

what is the conservation of energy

A

The total internal energy of an isolated system is constant; energy can be transformed from one form to another but can be neither created nor destroyed

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13
Q

what can we interconvert with thermodynamics

A

kinetic energy
chemical energy
heat
work
light
nuclear energy etc

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14
Q

what is an exothermic reaction

A

energy released to the surroundings as heat
q<0

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15
Q

what is an endothermic reaction

A

where the system takes in energy as heat
q>0

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16
Q

what happens when molecules are in uniform motion

A

energy transfered to the surroundings as work

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17
Q

what happens when molecules are in chaotic motion

A

energy transferred to the surroundings as heat

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18
Q

In thermodynamics, energy is

A

the capacity to do work

which is the transfer of energy that causes motion against an opposing force

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19
Q

in the piston example whats happening

A

the system is losing energy as work because its having to do work to lift the weight w<0
work is done by the system on the surroundings

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20
Q

whats an example of a reaction where w>0

A

h2 + O2 forming water, the system has gotten smaller (compressed)

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21
Q

What is the equation for work

A

work=distance.opposing force

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22
Q

what happens when a system does work

A

it stimulates orderly motion in the surroundings

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23
Q

what is the equation when gas expands

A

opposing force=PexA
=w=Pexh
=PexdeltaV=pgasdeltaV
but system loses energy so
w=-PexdeltaV
w=-deltanRT
only true when there is perfectly regversible expansion, constant pressure temp etc, perfectly at equilibrium

24
Q

what are the key assumptions for reversible expansion

A

no temp or pressure gradients
system at equilibrium throughout
process can be reversed wihotut losing energy
remember delta n=nfinal-ninitial

25
Q

what is internal energy (U)

A

it is a measure of all the energy reserves of a system
it is constant for an isolated system

26
Q

what is Um

A

it is the molar internal energy of a mole of our system Jmol^-1

27
Q

what is deltaU

A

=q + w

28
Q

What is enthalpy change of vapourisation

A

=-enthalpy change of condensation (under standard conditions)

29
Q

what is the standard enthalpy of formation

A

is when one mole of substance is formed from elements in their reference states, at a stated temperature (usually 298K)
the reference state is the most stable state at STP

30
Q

What is bond dissociation energy

A

it is defined as the enthalpy change when a specific bond in a compound dissociates

31
Q

What is bond energy BE or mean bond energy

A

it refers to the mean of the BDE values for similar bonds within a specific compound

32
Q

What is tabulated average bond energies ABE

A

usually apply to a type of bond across a range of related compounds
all calculations are estimations

33
Q

what is state function

A

it depends on the current state of the system, for example internal energy,
it is like a vector quantity so the route to get there doesnt matter

34
Q

what is an example of state functions

A

Gibbs free energy G=H-deltaTS
or enthalpy

35
Q

what is hess’s Law

A

The standard enthalpy change for a reaction is the sum of the standard changes for the reaction into which it can be divided

36
Q

What is the Zeroth Law

A

if two systems are each in thermal ewquilibrium with a third, they are inn thermal equilibrium with each other

37
Q

Features of a bomb calorimeter

A

used to measure temp changes at a constant volume V, w=0 so deltaU=q
it is an isolated adiabatic system
1 measure heat involved by reaction
2 use electricity to effect the same temp change

38
Q

what is the equation for delta U in an open system

A

=q + w
=q + pdeltaV

39
Q

What are factors used to compare fuels

A

Economic (price, weight, volume)
Environmental (CO2,NO2,O3,particulate (not always complete combustion)

40
Q

What is the carbon load of fuel

A

kg (of CO2 produed) per MJ energy

41
Q

What does a large carbon load mean

A

its a poor fuel (environmentally)

42
Q

what is the equation for energy densities

A

|deltacH|/RMM

43
Q

features of biofuels

A

agricultural or anaerobic digestion (contemporary biological processes)
potentially carbon neutral
larger alcohols (C4 C5) petrol replacements
biodiesels (methyl esters)

44
Q

what are some issues with biofuels

A

land use/food v fuel/soil erosion/ loss of biodiversity
poor fuel metrics
new chem/engineering

45
Q

what are some fuels for space flight

A

cryogenic fuels
hypergolic fuels

46
Q

what are some features of cryogenic fuels

A

H2 liquified and stored sub 33K
good fuel metrics

47
Q

Whats bad with cryogenic fuels

A

storage
hazardous
needs O2 supply

48
Q

features of hypergolic fuels

A

2 component propellant combo that spontaneously ignites
no need for air
liquid at 290k
near instant conversion of energy to heat and work
no need for ignition control

49
Q

whats problems with hypergolic fuels

A

highly corrosive and toxic
lots more chemistry to research and understand

50
Q

What is heat capacity

A

heat supplied/temp change
it tells us about what is happening to the energy in molecular terms
water has a large specific heat capacity which has a huge impact on the climate

51
Q

what is another equation for delta H

A

CpdeltaT

52
Q

what is another equation for deltaU

A

CvdeltaT
where ideal gases all have the same Cv 12.5JK-1mol-1
polyatomics have large Cv bvalues characteristic of molecule

53
Q

what is enthalpy change of solution

A

the heat exchanged at a constant pressure upon changing to a aq phase

54
Q

what is kirchhoffs law

A
55
Q

what is the equation for molar heat capacity

A

Cm=q/ndeltaT

56
Q

what is the equation for specific heat capacity

A

Cs=q/mdeltaT

Chemistry sem 1 (3 decks)

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