thermochemistry terms Flashcards
energy
the capacity of doing work or producing heat
kinetic energy
the energy of motion
Ek = ½ mv2
chemical potential energy
the energy stored in chemical bonds
composition or position
heat
energy that flows across a temperature gradient from hot to cold (q)
Flows from high-temperature areas to low-temperature areas
temperature
the measure of the average kinetic energy of the molecules in a system
system
part of the universe in which we are interested in.
surroundings
consists of the rest of the universe (although sometimes we can limit the surroundings to a smaller area immediately surrounding the system)
Burning a match
System: wood that Wood that’s burning
Surroundings: everything around the wood
first law of thermodynamics
Energy cannot be created or destroyed. It can only be converted from one form to another
Also known as the law of conservation of energy
Another way to desc this is to say that the energy of the universe is a constant
internal energy
An energy form inherent in every system
arises from the molecular state of motion of matter.
The symbol U is used for the internal energy and the unit of measurement is the joules (J)
delta E = q + w
enthalpy
Enthalpy is the measurement of energy in a thermodynamic system.
all of the energy in a system
delta H or q
calorimeter
a device used for heat measurements necessary for calorimetry. It mainly consists of a metallic vessel made of materials which are good conductors of electricity such as copper and aluminium etc.
calorimetry
the measurement of the transfer of heat into or out of a system during a chemical reaction or physical process
endothermic process
A process that absorbs heat from the surroundings
POSITIVE!!
exothermic process
A process that releases heat tot he surroundings
NEGATIVE
q positive (+)
Heat flows from surroundings to system; heat is absorbed by system
q negative (-)
Heat flows from system to surroundings; heat is given off
W positive (+)
Work done on system by surroundings
W negative (-)
Work done by system on surroundings
fusion
solid to liquid
solidification
liquid to solid
vapourization
liquid to gas
condensation
gas to liquid
thermochemistry
The chemistry of heat and heat-associated chemical phenomena.
sublimation
solid to gas (dry ice)
deposition
gas to solid
intermolecular forces
Intermolecular forces are responsible for most of the physical and chemical properties of matter.
holds together the particles that make up liquids and solids
heat capacity
the amount of heat required to change a substance’s temperature by one degree.
specific heat capacity
the amount of heat per unit of mass that is needed to raise the temperature of the substance by 1 degree Celsius.
molar heat of vapourization
the energy needed to vaporize one mole of a liquid
heat of combustion
the amount of heat liberated when a given amount of the substance undergoes combustion
heat of reaction
the change in the enthalpy of a chemical reaction that occurs at a constant pressure
ΔH=q
molar heat of fusion
the amount of heat necessary to melt 1.00 mole of a substance at its
melting point
no temperature change!!
molar heat of solidification
the heat released by one mole of that substance as it is converted from a liquid to a solid
molar heat of solution
the heat absorbed or released when one mole of the substance is dissolved in water.
work
The expenditure of energy and how it is transferring
work and heat are ways of transferring energy from one system to another.
specific heat for water
4.18
enthalpy changes during bonds breaking phase change
gains energy!! endothermic!
enthalpy changes during bonds forming phase change
loses energy!! exothermic
change in potential and kinetic energy during heating up
Potential energy–constant
kinetic energy–increasing
change in potential and kinetic energy during phase change
potential energy–increasing
kinetic energy–constant
process behind an endothermic reaction
If strong bonds break, there will be a large increase in Ep
If, in turn, weak bonds form, there will be a small decrease in Ep
The net Ep will be greater
Therefore, ∆H reaction = (+)
process behind an exothermic reaction
A little, a small increase in Ep will break weak bonds
If strong bonds form, a lot of energy will be released relative to the amount of energy to break the bonds of reactants, therefore there will be a large decrease in Ep
Overall, there is more energy release than absorbed and a net decrease in Ep
standard state
- kPa pressure
25 C
