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# Minooka Atoms and Elements Part 1

## by Jeanne Erfft, teacher at Minooka on Sep 18, 2008

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## 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
• Two Classifications
• Potential Energy
• Kinetic Energy
• Potential 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 tank
• PE = mgh
• Kinetic energy
• 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
• Work is a force acting over a distance
• Another definition is “the ability to resist a natural tendency”
• w = fd
• State Function
• Important idea
• 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
• Temperature
• 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?
• Thermal Equilibrium
• 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
• Where:
• 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
• 212 o F A Lesson for Life
• At 211 o F water is very hot. It will burn.
• At 212 o F water becomes steam, and
• Steam can power a locomotive.
• The one degree makes all of the difference.