energy. ____________ – the ability to do work or produce heat ____________ energy – energy due...
TRANSCRIPT
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Energy
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Energy
• ____________ – the ability to do work or produce heat
• ____________ energy – energy due to composition or position of an object
• ____________ energy – the energy of motion
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Energy
• ____________ - SI unit for energy 1 J = 1 Kgm2 / s2
• ____________– amount of energy required to raise 1 g of water 1°C
• 1 cal = 4.18 J• 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
• ____________– the energy used to move an object against a force
• ____________– a push or pull on an object
• W = mgd = fd = PE
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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 ball 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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E
• E has 3 parts:1. A # indicating the magnitude
2. A sign (+/-) indicating the direction
3. A unit
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Thermochemistry
• ____________ - study of heat changes that accompany chemical reactions and phase changes.
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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
System Surroundings
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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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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
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Specific Heat
• ____________– the amount of heat required to raise the temperature of 1 g of a substance 1 °C
• The units for specific heat are ____• The specific heat of water (in a liquid form
is 4.18 J/g°C)• All substances have a particular specific
heat
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Specific heat equation
• q = mcT
• q = heat gained or lost (J)
• m = mass (grams) note that this is different than the energy calculations
• c = specific heat (J/g°C)
• T = change in temperature (°C) = Tf-Ti
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Specific heat calculations
• How much heat is required to raise 250 g of water from 22°C to 98°C?
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• A piece of metal with a mass of 4.68 g absorbs 256 J of heat when its temperature is increased by 182°C. What is its specific heat?
Specific heat calculations
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• 60.0 J of heat are applied to a 5.00 g sample of calcium (c = 0.647J/g°C). If the final temperature is 51.1°C, calculate the original temperature.
Specific heat calculations
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Calorimetry
• ____________ - insulated device used for measuring the amount of heat absorbed or released during a chemical or physical process.
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Calorimetry
• When using calorimetry, you are usually trying to determine the identity of an unknown metal by finding its specific heat
• The heat lost from the metal will be gained by the water
• -q metal = q water
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Calorimetry
• - q metal = q water
• - (m metal)(c metal)(T metal) = (m water)(c water)(T water)
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Calorimetry Examples
• A 58.0 g sample of a metal at 100.0 °C is placed in a calorimeter containing 60.0 g of water at 18.0 °C. The temperature of that water increases to 22.0 °C. Calculate the specific heat of the metal.
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• A piece of metal with a mass of 4.68 g at 135°C is placed in a calorimeter with 25.0 g of water at 20.0 °C. The temperature rises to 35.0 °C. What is the specific heat of the metal?
Calorimetry Examples
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More calorimetry
• 3.25 g Mg is placed into 125 mL of HCl. The initial temperature of the calorimeter is 18.5°C & the final temperature is 26.6°C. If the heat capacity of the calorimeter is 4.86 J/g°C, calculate the enthalpy of the reaction.