Heat and Energy
May 12, 2015
Heat and EnergyHeat and Energy
What is Energy?What is Energy?
Petroleum products “Energy Crisis”It is at the very center of our
existenceEnergy is the ability to do work or
produce heat
Petroleum products “Energy Crisis”It is at the very center of our
existenceEnergy is the ability to do work or
produce heat
Two ClassificationsTwo Classifications
Potential EnergyKinetic Energy
Potential EnergyKinetic Energy
Potential EnergyPotential Energy
Energy due to position or composition
Energy stored in chemical bonds of petroleum products
Examples: Water stored behind a dam, calories in a chocolate bar, gas in a gas tankPE = mgh
Energy due to position or composition
Energy stored in chemical bonds of petroleum products
Examples: Water stored behind a dam, calories in a chocolate bar, gas in a gas tankPE = mgh
Kinetic energyKinetic energy
Energy due to motion of the objectEnergy released or absorbed in a
chemical reactionDepends on mass and velocity
KE=1/2 mv2
Energy due to motion of the objectEnergy released or absorbed in a
chemical reactionDepends on mass and velocity
KE=1/2 mv2
The internal motion of the particles in a body is its kinetic energy. Because these particles are vibrating back and forth they have a potential energy as well. The sum of the PE and KE of the particles is called the thermal energy of the object.
Remember that the kinetic theory says that a hot body has more thermal energy than a cold body.
The hot body has a higher total sum of PE and KE than a cold body.
Law of Conservation of Energy
Law of Conservation of Energy
Energy can be converted from one form to another….
But it can never be created or destroyed
Therefore, the energy of the Universe is CONSTANT
This is the First Law of Thermodynamics
Energy can be converted from one form to another….
But it can never be created or destroyed
Therefore, the energy of the Universe is CONSTANT
This is the First Law of Thermodynamics
WorkWork
Work is a force acting over a distance
Another definition is “the ability to resist a natural tendency”
w = fd
Work is a force acting over a distance
Another definition is “the ability to resist a natural tendency”
w = fd
State FunctionState Function
Important ideaIs a property of a system that changes
independently of it’s pathwayExample: You are traveling from Chicago
to DenverWhich property is a state function, Distance
traveled or change in elevation?
Important ideaIs a property of a system that changes
independently of it’s pathwayExample: You are traveling from Chicago
to DenverWhich property is a state function, Distance
traveled or change in elevation?
State Function Con’tState Function Con’t
Change in elevation is a state function because it doesn’t matter what path you take to get there
Distance traveled depends on the route you take, so distance traveled is not a state function
Change in Energy is a state function, work and heat are not.
Change in elevation is a state function because it doesn’t matter what path you take to get there
Distance traveled depends on the route you take, so distance traveled is not a state function
Change in Energy is a state function, work and heat are not.
Temperature and HeatTemperature and Heat
What is temperature?Temperature is a measure of the
random motions of the components of the substance
Must imagine this at the microscopic, molecular level
What is temperature?Temperature is a measure of the
random motions of the components of the substance
Must imagine this at the microscopic, molecular level
TemperatureTemperature
Two beakers of waterOne at 100 oC
Molecules moving fasterMore kinetic energy
One at 10 oCMolecules moving slowerLess kinetic energy
Two beakers of waterOne at 100 oC
Molecules moving fasterMore kinetic energy
One at 10 oCMolecules moving slowerLess kinetic energy
Same temp = same KE
Same temp = same KE
Heat vs. TemperatureHeat vs. Temperature
Heat is the flow of energy due to a temperature difference
Temperature is a measure of the average kinetic energy of the molecules
Heat is the flow of energy due to a temperature difference
Temperature is a measure of the average kinetic energy of the molecules
Heat flow is energy flowHeat flow is energy flow
Imagine two containers each holding the same amount of water. They are in contact with each other and heat can be transferred by water can not. No heat is lost to the surroundings. One side is at 100oC, and the other is at 10oC
Imagine two containers each holding the same amount of water. They are in contact with each other and heat can be transferred by water can not. No heat is lost to the surroundings. One side is at 100oC, and the other is at 10oC
Which way does heat flow?
Which way does heat flow?
When does heat stop flowing?
When does heat stop flowing?
Thermal EquilibriumThermal Equilibrium
When two objects in thermal contact cease to exchange energy by heat flow.
When two objects in thermal contact cease to exchange energy by heat flow.
Zeroth Law of Thermodynamics
Zeroth Law of Thermodynamics
Law of equilibriumTwo objects in thermal equilibrium
with each other are at the same temperature
Law of equilibriumTwo objects in thermal equilibrium
with each other are at the same temperature
Specific heat capacitySpecific heat capacity
Some definitions firstSystem: the part of the universe that
we are looking at (usually the chemical reaction)
Surroundings: everything else in the universe
Some definitions firstSystem: the part of the universe that
we are looking at (usually the chemical reaction)
Surroundings: everything else in the universe
Specific Heat Capacity Con’t
Specific Heat Capacity Con’t
The amount of energy required to change the temperature of a substance by 1 oC
Depends on the substanceDifferent substances respond
differently to being heatedExample: water, metal
The amount of energy required to change the temperature of a substance by 1 oC
Depends on the substanceDifferent substances respond
differently to being heatedExample: water, metal
The calorimetry equationThe calorimetry equation
Q = s x m x TWhere:
Q is the amount of heat energys is the specific heat of the substance
(must look this up)m is the mass (of the sample of the
substance)T is the CHANGE in TEMPERATURE
Q = s x m x TWhere:
Q is the amount of heat energys is the specific heat of the substance
(must look this up)m is the mass (of the sample of the
substance)T is the CHANGE in TEMPERATURE
What???? Come again??What???? Come again??
Q has units of Joules or Caloriess has units of J/g-oC, or Cal/g-oC, or
J/g K m has units of grams. If it doesn’t,
you must change it to grams in order to use the specific heat
T is the change in temperature in degrees Celsius or Kelvins
Q has units of Joules or Caloriess has units of J/g-oC, or Cal/g-oC, or
J/g K m has units of grams. If it doesn’t,
you must change it to grams in order to use the specific heat
T is the change in temperature in degrees Celsius or Kelvins
212o FA Lesson for Life
212o FA Lesson for Life
At 211o F water is very hot. It will burn.
At 212o F water becomes steam, andSteam can power a locomotive.The one degree makes all of the
difference.
At 211o F water is very hot. It will burn.
At 212o F water becomes steam, andSteam can power a locomotive.The one degree makes all of the
difference.