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Topic: Matter & Energy

Topic: Matter & Energy. Aim: How can the amount of energy gained or lost by a system be calculated? Do Now: What Celsius temperature is the equivalent of 500K? HW: RB p. 66 #38-46 ON SEPARATE PAPER (calculations). Heat. Energy measured in Joules or calories Usually use Joules in here

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Topic: Matter & Energy

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  1. Topic: Matter & Energy • Aim: How can the amount of energy gained or lost by a system be calculated? • Do Now: What Celsius temperature is the equivalent of 500K? • HW: RB p. 66 #38-46 ON SEPARATE PAPER (calculations)

  2. Heat • Energy measured in Joules or calories • Usually use Joules in here • Calorie??

  3. Heat Equation • Measures how much heat energy is absorbed or released in a system when a substance is warmed or cooled • Ref. Table T • Q = mCΔT • Q = energy (Joules) • m = mass • C = specific heat capacity (given on Table B for water) • ΔT = change in temperature (Tf – Ti) • THIS EQUATION CAN ONLY BE USED WHEN TWO TEMPERATURES ARE GIVEN IN THE PROBLEM!!!

  4. Physical Constants for Water • Focus on Specific Heat Capacity first

  5. Specific Heat Capacity • Amount of heat needed to raise the temperature of 1g of a substance by 1oC • Cwater = 4.18J/g.oC (on Table B) • This means that if I have 1g of water, I have to add 4.18J of energy to it to raise the temperature 1oC. • Considering small size of H2O molecule, this # is high • WATER RESISTS CHANGES IN TEMP!!

  6. Practice Problems • What is the total number of joules of heat energy absorbed by 15 grams of water when it is heated from 30°C to 40°C? • What is the total # of Joules lost when 10g water at 80 degrees is cooled to 60 degrees? • What is the total # of Joules of heat absorbed when the temp of 200g water is raised from 10 to 40 degrees? • How many Joules of heat are absorbed in raising the temp of 10g of water by 15 degrees?

  7. Practice Problems • A sample of water is cooled from 45 degrees to 35 degrees by the removal of 84 Joules of heat. What is the mass of the water? • A sample of water is heated from 10 to 15 degrees by the addition of 126 Joules of heat. What is the mass of the water?

  8. Practice Problems • 50 grams of water absorbs 4200 Joules of heat. What is the change in temperature? • What is the temperature change if 80 grams of water absorbs 1680J of energy? • When a 500g sample of water at 19 degrees absorbs 8400J of heat, the final temperature of the water will be…? • A 36g sample of water has an initial temperature of 22 degrees. After the sample absorbs 1200J of heat, the final temperature of the sample is…?

  9. Practice Problems • The specific heat of ethanol is 2.46 J/goC.  Find the heat energy required to raise the temperature of 193 g of ethanol from 19oC to 35oC.

  10. Other Heat Problems • What if the substance is changing phase? • What if the question states that temperature is constant? • YOU CANNOT USE Q=mCΔT!!! • BECAUSE THERE IS NO ΔT!!

  11. Heat of Fusion • amount of energy required to melt or freeze (crystallize) 1 gram a solid, Hf. • Table T for equation, Table B for Hf value • Q = mHf • NOTICE – THERE IS NO TEMP. CHANGE LISTED – BECAUSE THE TEMP. REMAINS CONSTANT DURING A PHASE CHANGE! • DO NOT FORGET THIS! • YOU HAVE BEEN WARNED! • Now, let’s do some practice problems.

  12. Sample Problems • How much energy is required to completely melt 31.5 g of H2O at its melting point of 0 °C? • How much energy must be removed to freeze 53.1 g of H2O at 0 °C? • How much heat energy is absorbed when 10 g ice melts to form liquid water at constant temperature?

  13. Heat of Vaporization • amount of energy required to evaporate (vaporize) or condense 1 gram of a liquid, Hv. • Table T for equation, Table B for Hv value • Q = mHv • NOTICE – THERE IS NO TEMP. CHANGE LISTED – BECAUSE THE TEMP. REMAINS CONSTANT DURING A PHASE CHANGE! • BY NOW, YOU SHOULD SEE THAT THIS IS IMPORTANT! • Shall we practice? We shall.

  14. Sample Problems • How many joules of energy are required to completely vaporize 49.5g of H2O at its boiling point? • 80.1 g of H2O exists as a gas at 100°C. How much energy must be removed to condense the steam into liquid? • How much heat is absorbed when 70 g of water is completely vaporized at its boiling point?

  15. Sample Problems • What is the total # of joules of heat energy absorbed when 10 grams of water is vaporized at its boiling point? • How much heat in joules is released when the temperature of 10 grams of water is changed from 15.5 degrees Celsius to 14.5 degrees Celsius? • How much heat energy is absorbed when 55g of ice melts to form liquid water?

  16. Practice Problems • The specific heat of ethanol is 2.46 J/goC.  Find the heat energy required to raise the temperature of 193 g of ethanol from 19oC to 35oC. • What is the total number of joules of heat energy absorbed by 15 grams of water when it is heated from 30°C to 40°C? • 10 • 63 • 150 • 630

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