Chapter 8 & 10 Flashcards
Evaporation
- liquid –> gas
- heat/ energy is required to overcome strong forces in liquid (therefore endothermic)
heat of vaporization/ enthalpy of vaporization
energy required to vaporize 1 mole of liquid at 1 atm of pressure
heat vaporization for water
2260 joules per gram
condensation
gas –> liquid
equilibrium vapour pressure
pressure of vapour present at equilibrium
sublimes
solid –> gas
heat curve
plot of temperature versus time for a process where energy is added at a constant rate
heating curve for water
- energy is added
- vibrations of water molecules increase as temperature rises
- molecules break loose from position
- goes from solid to liquid (plateau at 0 degrees) (all energy is used to disrupt the ice structure by breaking hydrogen bonds) (melting point)
- becomes completely liquid
- boiling point (100 degrees)
- energy added to vaporize liquid, temperature remains constant (100 degrees)
- liquid completely vapour
- temperature rises again
melting point
the temperature where a solid and liquid have the same vapour pressure where the total pressure is 1 atm
boiling point
- temperature at which the vapour pressure of liquid is exactly 1 atm
- 100 degrees
phase diagram
represents the phases of a substance as a function of temperature and pressure
triple point
- all three states of water are present
- solid and liquid water have identical vapour pressures
critical temperature
the temperature above which vapour cannot be liquidated no matter what pressure is applied
critical pressure
the pressure required to product liquefaction at the critical temperature
critical point
- critical temperature + critical pressure
- water = 374 degree at 218 atm
- for water it is liquid/vapour line
phase diagram for water
- melting point of ice decreases at external pressure increases (this happened because density of ice is less than that of liquid water at melting point)
- the solid/liquid boundary has a negative slope
- if pressure is increased and temperature is constant the ice will melt (increased pressure causes matter to reduce its volume) (ice has a larger volume than the same mass of liquid water)
phase diagram for water in ice skating
pressure from skate causes it to melt
phase diagram for water in lakes and rivers and stuff…
lower density of ice means that ice formed on rivers will float, giving a layer of insulation below
phase diagram for water in boiling water
- liquid boils where vapour pressure equals external pressure (depends on external pressure)
- at different elevations, water boils at different temperatures
phase diagram for carbon dioxide
- solid/liquid line is positive (solid carbon dioxide is more dense than liquid carbon dioxide)
- triple point: 5.1 atm, -56.6 degrees
- critical point: 72.8 atm and 31 degrees
- sublimes: -78 degrees
calorimeter
device used to determine the heat associated with a chemical reaction
calorimetry
- science of measuring heat
- based on observing the temperature change when a body absorbs or discharges energy as heat
- the amount of energy required depends on amount of substance present
molar heat capacity
- heat capacity per mole
- J/Celsius or J/K * mol
endothermic reaction
-absorbs heat from surroundings
-vaporization and fusion are some examples
decreased for surroundings (T is negative)(negative quantity)
-system has positive quantity
-enthalpy change is always POSITIVE
exothermic reaction
- releases heat to surroundings
- heat released results in a temperature increase for surrounds (T is positive)(positive quantity)
- heat released by system must have reverse sign (negative quanitity)
- enthanpy change is always NEGATIVE
heat of fusion
amount of heat that must be abosrbed to melt a speciic quantity of solid
heat content/ enthalpy
- stored energy
- the amount of heat transferred in a process depends on the difference in the energy stored in each substance
enthalpy change
the heat change that occurs at constant pressure
qp
- amount of heat transferred
- it depends on mass (m), heat (s), and temperature change (T)
specific heat of a substance
- it reflects its ability to absorb heat energy
- defined as the amount of heat needed to raise the temperature of one gram by one degree
specific heat of water
4.18 J/gC
temperature change (T)
equal to difference between final temperature and initial temperature
s
specific heat
normal boiling point
temperature at which the vapour pressure of the liquid is exactly 1 atm
melting
solid to liquid
evaporation
liquid to gas
freezing
liquid to solid
condensation (dew)
gas to liquid
sublimation
solid to gas
deposition
gas to solid
desntiy of liquid in dry ice
- there is a positive slope
- therefore the solid is denser than the liquid
