Minooka Atoms and Elements Part 1Presentation Transcript
Heat and Energy
What is Energy?
Petroleum products “Energy Crisis”
It is at the very center of our existence
Energy is the ability to do work or produce heat
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 tank
PE = mgh
Energy due to motion of the object
Energy released or absorbed in a chemical reaction
Depends on mass and velocity
KE=1/2 mv 2
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
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
Work is a force acting over a distance
Another definition is “the ability to resist a natural tendency”
w = fd
Is a property of a system that changes independently of it’s pathway
Example: You are traveling from Chicago to Denver
Which property is a state function, Distance traveled or change in elevation?
State 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.
Temperature 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
Two beakers of water
One at 100 o C
Molecules moving faster
More kinetic energy
One at 10 o C
Molecules moving slower
Less kinetic energy
Same temp = same KE
Heat 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 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 100 o C, and the other is at 10 o C
Which way does heat flow?
When does heat stop flowing?
When two objects in thermal contact cease to exchange energy by heat flow.
Zeroth Law of Thermodynamics
Law of equilibrium
Two objects in thermal equilibrium with each other are at the same temperature
Specific heat capacity
Some definitions first
System: 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
The amount of energy required to change the temperature of a substance by 1 o C
Depends on the substance
Different substances respond differently to being heated
Example: water, metal
The calorimetry equation
Q = s x m x T
Q is the amount of heat energy
s 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??
Q has units of Joules or Calories
s has units of J/g- o C, or Cal/g- o C, 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