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Energy
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Energy
• ___________ – the ability to do work or produce heat
• Energy exists in two different forms – ___________ energy & ___________ energy
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Potential Energy
• ___________– energy due to composition or position of an object
• Potential energy is ___________ energy that results from the attractions or repulsions of other objects
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Kinetic Energy
• ___________– energy of motion
• Kinetic energy depends on as objects ___________ & its ___________
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Energy
• A roller coaster at the top of a hill has a great amount of potential energy.
• As the rollercoaster begins to speed down the hill, the potential energy is turned into kinetic energy
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Energy
• The SI unit for energy is the ________ (J)
• 1 J = 1 Kgm2 / s2
• Another unit of energy is the ___________
• ___________– amount of energy required to raise 1 g of water 1°C
• 1 cal = 4.18 J
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Energy
• The calories that you eat are actually kilocalories or Calories (with a big C)
• 1000 calories = 1 Kilocalorie = 1 Calorie
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Energy Conversions
• Convert 15,500 joules into Calories
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Formulas – Kinetic Energy
• KE = ½ mv2
• KE = kinetic energy (joules)
• m = mass (must be in Kg)
• V = velocity (must be in m/s)
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Formulas – Potential Energy
• PE = mgh
• PE = Potential Energy (J)
• m = mass (Kg)
• g = gravitational constant = 9.8 m/s2
• h = height (m)
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Formulas - Work
• Work (w) – the energy used to move an object against a force
• Force (f) – a push or pull on an object
• W = mgd = fd = PE
• Work and potential energy can be looked at in the same light
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Examples
• A bowler lifts a 5.4 kg bowling ball 1.6m and then drops it to the ground.
• How much work was required to raise the ball?
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Examples
• How much potential energy does that ball have at this height?
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Examples
• If the bass is dropped and we assume that all of the potential energy is turned into kinetic energy, at what velocity will the bowling ball hit the ground?
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More examples
• What is the kinetic energy of 1 atom of Ar moving at 650 m/s?
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1st Law of Thermodynamics
• 1st Law of Thermodynamics – energy is conserved
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1st Law of Thermodynamics
• Since energy can neither be gained nor lost, the change in E can be calculated using:
• E = Ef – Ei
• In a chemical reaction i indicates reactants and f indicated products
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E
• E has 3 parts:1. A # indicating the magnitude
2. A sign (+/-) indicating the direction
3. A unit
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Thermochemistry
• ___________ is the study of heat changes that accompany chemical reactions and phase changes.
• The ___________ is the specific part of the universe that contains the reaction or process you wish to study.
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Thermochemistry
• Everything in the universe other than the system is considered the ___________ .
• Therefore, the ___________ is defined as the system plus the surroundings.
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Relating E to heat & work
• The system can exchange energy with its surroundings in 2 ways: as heat or work
• E = q + w
• E = change in energy
• q = heat
• w = work
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q & w
• Don’t forget q & w must have signs
• In order to get the sign you must look at the system as a box and the surroundings as everything else
SystemSurroundings
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q & w
• Anything going INTO the box will be +
• Anything going OUT of the box will be –
+-
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q & w
• If heat is transferred from the surroundings to the system and work is done on the system what are the signs for q & w?
q = +
w = +
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q & w
If heat is lost to the surroundings and work is done on the system what are the signs for q & w?
q = -
w = +
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Summary for q & w
• q + = heat into system
• q - = heat into surroundings
• w + = work done on the system
• w - = work done on the surroundings
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Examples
• A system loses 1150 J of heat to the surroundings and does 480 J of work on the surroundings. Calculate E.
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Examples
• A system absorbs 140 J of heat from the surroundings and does 85 J of work on the surroundings. Calculate E.
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Endothermic & Exothermic
• ___________ system absorbs heat Heat flows into the system Temperature goes down
• ___________ Heat flows out of the system and into the
surroundings Temperature goes up
• Only look at heat (q) to determine if the system is endo or exo