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HEATING CURVES

HEATING CURVES . What are some things that happen as we heat a sample up?. Solid  Liquid  Gas Melting, Evaporating Increase in entropy (what is entropy?). What is heat? How is heat different from temperature? . Heat is a measure of kinetic or translational energy

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HEATING CURVES

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  1. HEATING CURVES

  2. What are some things that happen as we heat a sample up? • Solid  Liquid  Gas • Melting, Evaporating • Increase in entropy (what is entropy?)

  3. What is heat? How is heat different from temperature? • Heat is a measure of kinetic or translational energy • In chemistry heat is measure in Joules (J) • Heat is dependent on mass, temperature change and specific heat capacity • Temperature is a measure the average kinetic energy of a substance • Temperature is independent of heat • Temperature is measured in Kelvin (K) or Celsius (C)

  4. What is the heating curve? • The heating curve is a graph which represents how a sample changes phases. As heat is added over time, the sample changes temperature and phase accordingly. It allows us to visualize the changes in matter that we’ve been calculating thus far. Melting

  5. How does the heating curve look?

  6. What are the parts of the heating curve?

  7. What are the parts of the heating curve?

  8. Why is the heating curve flat at some portions? (BC and DE) • Temperature (KE) is staying constant, but PE is increasing • The matter is changing phase- solid is becoming liquid (BC) and liquid is becoming a gas (DE)

  9. How do we calculate the energy changes that occur on the flat portions? • We use heat of fusion (Hf) in segment BC and heat of vaporization (Hv) in segment DE. • (for BC) Q= mHf • (for DE) Q= mHv

  10. What is heat of fusion? What is heat of vaporization? • Hf is the amount of energy needed to completely make a solid into a liquid • Hv is the amount of energy needed to completely make a liquid into a gas • In both cases you are adding enough energy to overcome the forces of attraction betweeen the molecules

  11. Calculations Constants needed are: CH2O = 4.18 J/gK, Cice= 2.06 J/gK, Csteam= 2.00 J/gK,Hf = 334J/g, Hv= 2260 J/g You have a 23.0 g sample of H2O at 227K. How many joules if heat energy are necessary to: Heat the ice to 273K? Melt the ice? Heat the water to 373K? Boil the water? Heat the steam from 373K to 381K? Locate each part of the question on the curve

  12. Solution Heat the ice to 273K? Q=mC∆T Q= ? m= 23.0 g C= 2.06J/gK ∆T = 273K- 227K = 46K Q= 23.0g x2.06 J/gK x 46K= Q= 2180J

  13. Solution Melt the ice? Q= mHf m= 23.0g Hf= 334 J/g Q= 23.0g x 334 J/g Q= 7,682 J

  14. Solution c. Heat the water to 373K Q=mC∆T Q= ? m= 23.0 g C= 4.18J/gK ∆T = 373K -273K = 100K Q= 23.0g x4.18J/gK x 100K= Q= 9614J

  15. Solution d) Boil the water Q= mHv Q= ? m= 23.0g Hv = 2260 J/g Q= 23.0g x 2260J/g Q= 51,980J

  16. Solution e) Heat the steam from 373K to 381K Q=mC∆T Q= ? m= 23.0 g C= 2.00J/gK ∆T = 381K -373K = 8K Q= 23.0g x 2.00J/gKx 8K= Q= 368J

  17. Solution e d c b a f) locate each part of the question on the curve

  18. Summary • The heating curve is a useful tool to show us the changes in temperature, energy, and entropy as a sample is heated up. It give us detailed information about phases and phase changes of samples.

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