Transcript Thermal Energy Transfer in the Hydrosphere

Thermal Energy Transfer in the
Hydrosphere
Section 2.3
Objectives
• Define specific heat capacity and use it to
calculate thermal energy
• Describe the hydrological cycle
• Distinguish between different phases of the
hydrological cycle
• Calculate heat of fusion and heat of vaporization
Specific Heat Capacity
• Symbolized as “c”
• Amount of energy needed to raise temp of 1 g of
a substance by 1 degree Celsius
• Water c= 4.19 J/g degree Celsius
▫ This is high
• What effect might this have on the climate of
Vancouver compared to Calgary?
Calculating thermal energy
Q = mcΔt
Q= amount of thermal energy (Joules)
m = mass of substance in grams (g)
c = specific heat capacity (J/g°C)
t = change in temperature (°C)
Specific Heat Capacity
• Each substance
on earth has a
SHC.
Examples
• A house contains 170 g of dry air. The furnace
has broken, and the temperature of the air has
fallen to 2.0°C. How much energy is needed to
heat the air in the home back to 20°C.
Examples
• What is the mass of water that has its
temperature raised 35°C and absorbs 100 J of
energy?
Water
• Water has a very
large SHC for its
size.
• This is due to
some of the
properties that we
discussed in the
previous units.
▫ Hydrogen Bonds
▫ Dipoles
Oceans and Mountains Influence
Climate
• How do these geological
features affect weather?
▫ When moist air cools, it
cannot hold as much water
which may fall in the form of
precipitation.
▫ Warm air rises and cool air
replaces it this causes the
movement of air.
How Oceans Distribute Heat
• Oceans are a great storage of
heat.
▫ Low albedo
▫ Absorb 90% of incoming
solar energy
▫ Large specific heat capacity
▫ Cover lots of the earth’s
surface
Oceans and Mountains Influence
Climate
• Because water has a higher SHC
its temperature changes slower.
• During the day air over the land
warms faster and flows out to
sea while the cooler sea air
comes in to replace it.
• This is called a sea breeze.
Oceans and Mountains Influence
Climate
• During the night the land cools
faster than the sea so warm air
from the sea rises and is
replaced by the cooler air from
the land.
• This is called a land breeze
Oceans and Mountains Influence
Climate
• Mountains provide a barrier
that forces air to rise over top of
them.
• As moist air rises it cools and
the water held in it condenses.
• This leaves very little moisture
in the air as it flows quickly
down the other side of the
mountain.
▫ Areas on the other side of the
mountain are in a rain shadow.
Practice
• A 50.0 g mass of water at 25.0 °C is heated to
50.0°C on a hot plate. Given that the theoretical
specific heat capacity of water is 4.19 J/g°C,
determine the value for Q
• Answer:
Practice
• How much thermal energy must be released to
decrease the temperature of 100 g of water by
10.0 °C, given that the theoretical specific heat
capacity of water is 4.19 J/g°C?
• Answer:
Practice
• Calculate the change in temperature that occurs
when 8380 J of thermal energy is added to
100.0 g of water. c= 4.19 J/g°C
• Answer:
Practice
• When 21.6 J of thermal energy is added to a 2.0
g mass of iron, the temperature of the iron
increases by 24.0°C. What is the experimental
specific heat capacity of iron?
Hydrological Cycle
• Water is constantly moving through the
biosphere
• Changing phases from solid to liquid to gas and
back again
• Uses evaporation, condensation, transpiration,
and precipitation
• Add or release thermal energy for phase changes
Energy Transfer Types
• Heat of fusion
▫ Energy absorbed when 1 mol of a substance
changes from solid to liquid
• Heat of Solidification
▫ Energy released when 1 mol of a substance
changes from liquid to solid
• Heat of Vaporization
▫ Energy absorbed when 1 mol of a substance
changes from liquid to vapor
Energy Transfer Types cont…
• Heat of Condensation
▫ Energy released when 1 mol of a substance
changes from vapor to liquid
Energy Transfer Graph
Where on the graph
would we label heat of
fusion? Heat of
vaporization?
Phase Changes
• With specific heat
capacity that tells us
how much energy is
needed to raise the
temperature.
• When moving from
solid  liquid and
liquid  gas more
energy is required to
break bonds.
Heat of Fusion
• The amount of
energy required to
melt a substance is
referred to as the
heat of fusion.
• Q = nHfus
▫ Q = energy
required
▫ n = number of
moles
▫ Hfus = J/mol
Example
• A beaker contains 360.4 g of water in the solid
state at 0°C. How much energy is required to
convert the solid ice to liquid water?
Heat of Vapourization
• The amount of energy
required to move a
substance from liquid to
gas is referred to as the
heat of vapourization.
• Q = nHvap
▫ Q = energy required
▫ n = number of moles
▫ Hvap = J/mol
Example
• A beaker contains 360.4 g of water in the liquid
state at 100°C. How much energy is required to
convert the liquid water to water vapour?
Summary Chart
Energy
Transfer
Type
Phase
changes
Energy
absorbed or
released?
Calculating Heat of Fusion
Hfus = _Q_
n
Hfus = heat of fusion (kJ/mol)
Q = quantity of thermal energy (kJ)
n = amount of the substance (mol)
Practice
• When 27.05 kJ of thermal energy is added to
4.50 mol of ice at 0.0°C, the ice melts
completely. What is the experimental heat of
fusion of water?
• Answer:
Practice
• When 5.00 g of ice melts, 1.67 kJ of thermal
energy is absorbed. Calculate the experimental
heat of fusion of ice. The molar mass, M, of ice
is 18.02 g/mol.
• Answer:
Practice
• When 0.751 kJ of thermal energy is added to
0.125 mol of ice at 0.0°C, the ice changes phase.
Calculate the experimental heat of fusion of ice.
Calculating Heat of Vaporization
Hvap = _Q_
n
Hvap = heat of vaporization (kJ/mol)
Q = quantity of thermal energy (kJ/mol)
n = amount of the substance (mol)
Practice
• When 150 g of water changes from liquid to
vapor phase, 339 kJ of energy is absorbed.
Determine the experimental heat of vaporization
of water, given that the molar mass, M, of water
is 18.02 g/mol
• Answer:
Practice
• When 8.70 kJ of thermal energy is added to 2.50
mol of liquid methanol, all the methanol enters
the vapor phase. Determine the experimental
heat of vaporization of methanol.
Phase Changes and Global Energy
Transfer
• Phase changes in the hydrologic cycle play a role
in global transfer of thermal energy
• The transfer of energy warms the air, which rises
• This can cause thunderstorms or hurricanes