First Law of thermodynamics Flashcards
What are the surroundings
anything outside of the system
what confines the system
the system boundary
what is an isothermal change
when the system is closed which means the temp of the surroundings impacts the temp of the system
the wall is diathermal
exchanging heat
what is an adiabatic change
when there is no temp change in the closed system due to the surroundings
the wall is adiabatic
what is a thermodynamic system
it is part of the physical universe with a specified boundary for observation
What is the first law of thermodynamics
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
What is work done
work is done when a force is applied to an object and that causes that object to move a distance
what is an open system
if there can be matter and heat exchanged with the surroundings like a beaker without a bung or a human body
what is a closed system
if heat can still be exchanged but matter cannot like a beaker with a bung or a light bulb
what is an isolated system
neither heat nor matter can be exchanged, like a perfect thermal flask or bomb calorimeter
what is the equation for work done
deltaU=q + w
what is the conservation of energy
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
what can we interconvert with thermodynamics
kinetic energy
chemical energy
heat
work
light
nuclear energy etc
what is an exothermic reaction
energy released to the surroundings as heat
q<0
what is an endothermic reaction
where the system takes in energy as heat
q>0
what happens when molecules are in uniform motion
energy transfered to the surroundings as work
what happens when molecules are in chaotic motion
energy transferred to the surroundings as heat
In thermodynamics, energy is
the capacity to do work
which is the transfer of energy that causes motion against an opposing force
in the piston example whats happening
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
whats an example of a reaction where w>0
h2 + O2 forming water, the system has gotten smaller (compressed)
What is the equation for work
work=distance.opposing force
what happens when a system does work
it stimulates orderly motion in the surroundings
what is the equation when gas expands
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
what are the key assumptions for reversible expansion
no temp or pressure gradients
system at equilibrium throughout
process can be reversed wihotut losing energy
remember delta n=nfinal-ninitial
what is internal energy (U)
it is a measure of all the energy reserves of a system
it is constant for an isolated system
what is Um
it is the molar internal energy of a mole of our system Jmol^-1
what is deltaU
=q + w
What is enthalpy change of vapourisation
=-enthalpy change of condensation (under standard conditions)
what is the standard enthalpy of formation
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
What is bond dissociation energy
it is defined as the enthalpy change when a specific bond in a compound dissociates
What is bond energy BE or mean bond energy
it refers to the mean of the BDE values for similar bonds within a specific compound
What is tabulated average bond energies ABE
usually apply to a type of bond across a range of related compounds
all calculations are estimations
what is state function
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
what is an example of state functions
Gibbs free energy G=H-deltaTS
or enthalpy
what is hess’s Law
The standard enthalpy change for a reaction is the sum of the standard changes for the reaction into which it can be divided
What is the Zeroth Law
if two systems are each in thermal ewquilibrium with a third, they are inn thermal equilibrium with each other
Features of a bomb calorimeter
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
what is the equation for delta U in an open system
=q + w
=q + pdeltaV
What are factors used to compare fuels
Economic (price, weight, volume)
Environmental (CO2,NO2,O3,particulate (not always complete combustion)
What is the carbon load of fuel
kg (of CO2 produed) per MJ energy
What does a large carbon load mean
its a poor fuel (environmentally)
what is the equation for energy densities
|deltacH|/RMM
features of biofuels
agricultural or anaerobic digestion (contemporary biological processes)
potentially carbon neutral
larger alcohols (C4 C5) petrol replacements
biodiesels (methyl esters)
what are some issues with biofuels
land use/food v fuel/soil erosion/ loss of biodiversity
poor fuel metrics
new chem/engineering
what are some fuels for space flight
cryogenic fuels
hypergolic fuels
what are some features of cryogenic fuels
H2 liquified and stored sub 33K
good fuel metrics
Whats bad with cryogenic fuels
storage
hazardous
needs O2 supply
features of hypergolic fuels
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
whats problems with hypergolic fuels
highly corrosive and toxic
lots more chemistry to research and understand
What is heat capacity
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
what is another equation for delta H
CpdeltaT
what is another equation for deltaU
CvdeltaT
where ideal gases all have the same Cv 12.5JK-1mol-1
polyatomics have large Cv bvalues characteristic of molecule
what is enthalpy change of solution
the heat exchanged at a constant pressure upon changing to a aq phase
what is kirchhoffs law
what is the equation for molar heat capacity
Cm=q/ndeltaT
what is the equation for specific heat capacity
Cs=q/mdeltaT
