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Thermodynamics and Specific Heat

Thermodynamics and Specific Heat. Some Like it Hot and Some Sweat when the Heat is On!!!. First Law of Thermodynamics. All energy lost by one system must be gained by the surroundings (another system) System: A group of interacting objects and effects that are selected for investigation.

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Thermodynamics and Specific Heat

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  1. Thermodynamics and Specific Heat Some Like it Hot and Some Sweat when the Heat is On!!!

  2. First Law of Thermodynamics • All energy lost by one system must be gained by the surroundings (another system) • System: • A group of interacting objects and effects that are selected for investigation. • Surroundings: • Everything else except the system.

  3. Second Law of Thermodynamics • States energy (heat) spontaneously flows from higher temperature to lower temperature until it reaches thermal equilibrium. • A condition where the temperatures are the same and heat no longer flows Hot Coffee Heat Flow Heat Flow

  4. Specific Heat • The quantity of energy it takes per gram of a certain material to raise the temperature by one degree Celsius. • Symbol: cp • Units: J/g·℃

  5. Examples of Specific Heats • Water 4.184 J/g·℃ • Air 1.006 J/g·℃ • Aluminum 0.900J/g·℃ • Gold 0.129 J/g·℃ • Steel 0.470 J/g·℃

  6. Heat Equation • Used to calculate how much energy it takes to make a temperature change in a mass of material E = m·cp·(T2-T1) E = energy m = mass cp= specific heat T2= final temperature T1= starting temperature

  7. Example of Using Heat Equation 1. Calculate the amount of energy required to heat 15.5 g of water from 17℃ to 25 ℃.

  8. Another example – Let’s switch it up! 2. A scientist inputs 27,500 J of thermal energy into a sample of steel. The temperature increases from 15℃ to 75℃ . What is the mass of the steel?

  9. Review Problem #1 A 62.5-g piece of copper absorbs 6,140 J of energy when heated by a Bunsen burner. If the temperature of the copper increases from 21 °C to 310 °C, what is the specific heat of the metal?

  10. Review Problem #2 A 25.5 g sample of precious gold has an initial temperature of 15 °C. A flame transfers 378 J of thermal energy to the gold. What is the final temperature of the gold? (cp gold = 0.129 J/g·℃)

  11. Challenge Question: A hot piece of metal is dropped into 150-g with a starting temperature of 21 °C. The temperature of the water increased to 30 °C. • How much energy was needed to increase the temperature of the water? • Where did the energy come from? • If the metal has a mass of 47 g and a starting temperature of 200 °C, what is the specific heat of the metal? • Assume – all energy lost by metal = all energy gained by water • Assume – final temps of both are equal (thermal equilibrium)

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