Lectures 21-26 Flashcards
energy
quantitative property that provides the ability to ‘do work’ or ‘supply heat’
potential energy (locked-in energy)
stored energy
kinetic energy (movement)
energy in motion
thermodynamics
science of the relationship between heat and other forms of energy
1 J =
1 Nm
1 J =
1 kg m^2s^-2
calorie (cal)
energy required to raise the temperature of 1g of water by 1 degree Celsius (1 cal = 4.184 J)
Calorie (C)
used to represent energy content of our food; 1 C = 1000 cal
The Law of Conservation of Energy
energy can be converted from one form into another, but it CANNOT be created or destroyed. The total energy of the universe is constant
universe
system + surrounding
open system
matter can be transferred through opening in the flask; heat can be conducted through flask walls
closed system
flask is stoppered so no matter can be transferred; heat can be conducted through the flask walls
isolated system
heat transfer is prevented by the vacuum flask; matter cannot be transferred
isothermal change
heat is exchanged between system and surroundings, so their temperatures are equal
adiabatic change
no heat exchange between system and surroundings, so their temperatures may not be equal
heat (q)
energy transferred from one system to another due to a temperature difference
temperature (T)
measure of ‘how hot’ something is (kinetic energy) and ability to transfer heat to other systems or surroundings
extensive property
a property of matter that changes as the amount of matter changes
is heat an extensive or intensive property?
extensive
intensive property
property of matter that does not change as the amount of matter changes
is temperature an extensive or intensive property?
intensive
work (w)
involves energy exchange as a result of motion against an opposing force (F)
work equation
w = Fd
when a system does work on the surroundings,
it loses energy
when the surroundings do work on the system,
it gains energy
volume work equation
w = -p(Ext)deltaV where p(ext) is external pressure
endothermic reaction
chemical process that absorbs heat
exothermic reaction
chemical process that releases heat
activation energy
energy required to break the bonds of the reactants
state functions
depend only on the amount of substance and its conditions; pathway does not matter
internal energy (U)
the sum of all its kinetic and potential energies of all the atoms, ions and molecules within the system
internal energy is an
extensive property and a state function
deltaU equation
deltaU = U(final) - U(initial)
change in internal energy in a closed system
deltaU = q + w
system gains internal energy
deltaU > 0
system loses internal energy
deltaU < 0
K and Celsius interchangeable for
SHC calculations
enthalpy change (deltaH)
equal to the heat transferred between the system and surroundings during a process that occurs at constant pressure
heat transferred under constant pressure
q(p) (deltaH = q(p))
enthalpy is a
state function
deltaH for exothermic
< 0
deltaH for endothermic
> 0
relationship between internal energy and heat gained/lost
deltaH = deltaU + pdeltaV
for systems containing no gases, deltaH
approximately equals deltaU
for systems containing gases, deltaH
= deltaU + deltan(gas)RT
molar enthalpy change of fusion/latent heat of fusion
energy required to melt 1 mol of a pure substance at its melting point
molar enthalpy change of vaporisation/latent heat of vaporisation
energy required to vaporise one mole of a pure substance at its boiling point
molar enthalpy change of fusion for water
6.00 kJ mol^-1
molar enthalpy change of vaporisation for water
40.65 kj mol^-1
heat capacity
tells us how much heat energy we need to put into a substance to raise its temperature
specific heat capacity (Cs)
heat needed to raise the temperature of 1g of substance by 1 K
specific heat capacity equation
Cs = q/mdeltaT
molar heat capacity (Cm)
heat required to raise the temperature of 1 mol of substance by 1 K
molar heat capacity equation
Cm = q/ndeltaT
for gases, heat capacity depends on whether measurement is carried out at
constant pressure (Cp) or constant volume (Cv)
molar heat capacity at constant pressure
Cp = q(p)/ndeltaT J K^-1 mol^-1
molar heat capacity at constant volume
Cv = q(v)/ndeltaT J K^-1 mol^-1
enthalpy change of a reaction (deltarH)
the difference between the sum of enthalpies of the products and the sum of enthalpies of the reactants