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Energetics

Energetics. Topic 5. Specific heat is the amount of heat per unit mass required to raise the temperature of a substance by one degree Celsius. Q = mc ∆T. Specific heat is the amount of heat per unit mass required to raise the temperature of a substance by one degree Celsius. Q = mc ∆T.

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Energetics

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  1. Energetics Topic 5

  2. Specific heat is the amount of heat per unit mass required to raise the temperature of a substance by one degree Celsius. Q = mc∆T

  3. Specific heat is the amount of heat per unit mass required to raise the temperature of a substance by one degree Celsius. Q = mc∆T Joules grams degrees K

  4. heat energy = m c ∆T (K or C) Note that the magnitude of degrees Kelvin is the same as degrees Celsius.

  5. For water: = Joules grams 4.18 degrees K

  6. For water: = Joules kilograms 4180 degrees K

  7. Bomb Calorimeter

  8. Calorimeter

  9. Example: If a reaction takes place in the water. Heat of reaction = Q = mc∆T Heat of reaction is in Joules, and a measure of ENTHALPY CHANGE

  10. Example: If a reaction takes place in the water. Heat of reaction = Q = mc∆T Heat of reaction is in Joules, and is a measure of ENTHALPY CHANGE So if you know how many moles reacted, = ENTHALPY CHANGE of Reaction (∆H) Joules moles

  11. Example: If a heated substance is placed in the water. Heat lost by the substance = heat gained by the water. mc∆T = mc∆T

  12. Example: If a heated substance is placed in the water. Heat lost by the substance = heat gained by the water. mc∆T = mc∆T

  13. Experiment: Find the specific heats of various metals IB assessment: Conclusion & Evaluation

  14. Enthalpy ( H for Heat Energy or Heat ) is the Energy contained in a substance. It cannot be measured.

  15. CO2 H2O But a CHANGE in Enthalpy can be measured. ∆H ( ∆ means ‘change in’ )

  16. CO2 H2O But a CHANGE in Enthalpy can be measured. ∆H ( ∆ means ‘change in’ ) And it is NOT the change in temperature

  17. H of products - H of reactants = ∆H CO2 H2O The final ∆H of the reaction may be positive or negative.

  18. Bond-breaking and bond-making: Which is exothermic and which is endothermic?: http://www.cdli.ca/courses/chem3202/unit03_org02_ilo01/b_activity.html

  19. The final ∆H of the reaction may be positive or negative.

  20. Hess’s Law

  21. HCl(aq) + NaOH(s)  Na+(aq) + Cl-(aq) + H2O

  22. HCl(aq) + NaOH(s)  NaCl(aq) + H2O(l) NaOH(s)  NaOH (aq) HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)

  23. HCl(aq) + NaOH(s)  NaCl(aq) + H2O ∆H1 NaOH(s)  NaOH (aq) ∆H2 HCl(aq) + NaOH(aq) NaCl(aq) + H2O ∆H3 ∆H1= ∆H2 + ∆H3

  24. Do this experiment in a Calorimeter

  25. Do this experiment in a Calorimeter • Add: • 2.00g NaOH to 0.1000L 0.500M HCl • 2.00g NaOH to 0.1000L Distilled Water • 3. 0.0500L 1.00MNaOH to 0.0500L 1.00M HCl

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