Section C: thermodynamics Flashcards
what is the first law of thermodynamics?
energy is conserved ie. it cannot be created or destroyed
define ‘specific heat capacity’
the energy required to increase the temperature of 1g of water by 1C (= 1 calorie)
what is the relationship between calories and joules?
1 cal = 4.2 J
which combination of units is equal to 1 Coulomb?
1 C = 1 A.s
which combination of units is equal to 1 Volt?
1 V = 1 J.C^-1
what is the evidence for the first law of thermodynamics?
Joule’s Paddlewheel experiment showing the equivalence of work and heat
how is work done calculated?
E = Fx
where F = force; x = distance
define ‘specific latent heat’
the amount of energy in the form of heat required to effect a phase change in 1 kg of a substance without any change in temperature
how can the specific heat capacity be calculated from a graph of energy versus temperature?
it is equal to the gradient of the graph
what graph can be drawn to calculate the specific heat capacity?
energy versus temperature plot
what is the metabolic rate?
the rate of energy conversion ie. power dispersed
P = dE/dt
what is Kleiber’s Law?
P ∝ M^3/4
where P = metabolic rate; M = mass
what is the relationship between horsepower and Watts?
1 hp = 745.1 W
what is an open system?
exchange of energy and matter with the surroundings
what is a closed system?
exchange of energy but not of matter with the surroundings
what is an isolated system?
no exchange of energy or matter with the surroundings
what is an adiabatic system?
no exchange of heat with the surroundings
true or false: the Maxwell-Boltzmann distribution is symmetrical
false; it is asymmetrical and weighted towards lower speeds
what is the Boltzmann distribution function?
population En / population E0 = e^ -(En-E0) / kT
what is ‘k’?
Boltzmann’s constant
k = 1.38 x 10^-23 J.K^-1
what is the zeroth law of thermodynamics?
energy flows in the form of heat between objects to equalise their temperature if T(A) = T(B) and T(B) = T(C), then T(A) = T(C)
is temperature an intensive or extensive property?
intensive
define ‘intensive’ property
not additive; does not depend on the amount of material
define ‘internal energy’, U
the sum of all possible energies in the system
define ‘extensive’ property
additive; depends on the amount of material
since the absolute value of U cannot be determined, what calculation is performed instead?
ΔU = q + w
where q = heat transferred to the system; w = work done on the system
what is ‘q’?
heat transferred TO the system
what is ‘w’?
work done ON the system
what is a state function?
the value does not depend on the path taken to reach the specific value
what is the opposite of a state function?
a cell path function
what are boundary phenomena?
energy is transferred across the system-surroundings boundary
give two examples of boundary phenomena
q and w
define ‘heat’
the transfer of energy due to a difference in temperature between the system and surroundings, resulting in a change in the random motion at the atomic level
define ‘work’
the transfer of energy to/from the system that results in the coherent or coordinated motion of the molecules of a system
how is work done minimised?
it is minimised if carried out reversibly ie. by infinitesimally small steps
what does it mean if q > 0 ?
endothermic
energy transfer from surrounding to system
what does it mean if q is less than 0?
exothermic
energy transfer from system to the surroundings
what does it mean if w > 0 ?
the surroundings do work ON the system ie. the system gains energy
what does it mean if w is less than 0?
the system does work ON the surroundings ie. the system loses energy
how is work done minimised?
it is minimised if carried out reversibly ie. by infinitesimally small steps
how else can work be written?
work = - pΔV = - Fx = - pAx
how else can ΔU = q + w be written? what assumption does this rely on?
ΔU + pΔV = ΔH
at constant pressure, if volume does not change, q(p) = ΔH
when volume and pressure are constant, what does the change in internal energy equal?
ΔU ≈ ΔH
when volume and pressure are constant, what does the work done equal?
q(p) = ΔH
define ‘enthalpy change’
the difference in energy used to break bonds in a chemical reaction and energy gained by the formation of new bonds
what is meant if ΔH > 0 ?
the reaction is endothermic
what is meant if ΔH is less than 0?
the reaction is exothermic
describe the nature of enthalpy
- state function
- extensive and additive
- the absolute value cannot be measured, only differences
- changes in pressure, temperature, etc. result in changes in H
what information is provided by entropy?
the direction of spontaneous change
what are the units of entropy?
kJ.mol^-1.K^-1
what is the relationship between entropy, heat/energy change and temperature?
ΔS ≥ q/T
where q = heat/energy change; T = temperature
how is entropy minimised?
it is minimised if carried out reversibly ie. by infinitesimally small steps
what is the relationship between ΔS(cold) and ΔS(hot)?
|ΔS(cold)| > |ΔS(hot)|
since ΔS(cold) > 0; ΔS(hot) is less than 0
what is the relationship between ΔS(cold) and ΔS(hot) when the reaction is reversible?
ΔS(cold) + ΔS(hot) = 0
which of ΔS(hot) and ΔS(cold) is less than zero, and which is greater?
ΔS(cold) > 0
ΔS(hot) is less than 0
what is the second law of thermodynamics?
- the entropy of the universe will increase over time
- in any spontaneous process, the entropy will increase
- the entropy of the universe is never negative
what is the third law of thermodynamics?
- for any perfect crystal, at T = 0, the entropy is zero
- entropy increases with degrees of freedom and molecular size
what is the Boltzmann equation?
S = klnW
what is the mole fraction?
moles of A / total moles of everything
what is molality?
moles of solute / mass of solvent
units mol.kg^-1
what is the relationship between molality and the mole fraction?
molality ∝ mole fraction
what is meant by biological systems being isothermal?
they do not rely on changes in temperature to do work
how is the Gibbs free energy calculated?
ΔG = ΔH - TΔS
requiring fixed pressure and temperature
what are the requirements for measuring ΔG?
fixed pressure and temperature
what is meant by μ?
chemical potential = the measure of how Gibbs energy changes per molecule of substance
when is the chemical potential highest?
for a pure liquid
what is indicated by differences in μ?
in which direction molecules move
what is the chemical potential for a gas, A?
μ(A) = μ0(A) + RTlnP
where P = pressure
what is the chemical potential for a liquid, A?
μ(A) = μ0(A) + RTlnx(A) where x(A) is the mole fraction
what is the relationship between ΔG and the equilibrium constant, k?
ΔG = - RTlnk
what is osmotic pressure proportional to?
osmotic pressure (π) ∝ molarity
how is the osmotic pressure calculated?
π = iMRT
where i is the dimensionless van’t Hoff factor; M = molarity; R is the gas constant = 0.082 L.atm.K^-1.mol^-1; T = temperature
what are the units of osmotic pressure?
atm
what is the van’t Hoff formula?
π = iMRT
