1 / 20

Chapter 12

Chapter 12. Section 4 – Calorimetry. Calorimetry. the study of heat flow and heat measurements. How to determine the enthalpy change?. C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O Δ H o =-2803 kJ. Calorimeter. A completely insulated container – no energy can’t go in or come out.

ojal
Download Presentation

Chapter 12

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 12 Section 4 – Calorimetry

  2. Calorimetry • the study of heat flow and heat measurements

  3. How to determine the enthalpy change? • C6H12O6+ 6O2 6CO2 + 6H2O ΔHo=-2803 kJ

  4. Calorimeter • A completely insulated container – no energy can’t go in or come out

  5. Conservation of Energy • amount of energy released by a chemical reaction = amount of energy absorbed by water • qreaction = ‒qwater • water = surrounding

  6. Heat Transfer (Q) Calculation (Example) A 5.10-kg cast-iron skillet is heated on the stove from 295 K to 450 K. How much heat had to be transferred to the iron? CFe = 0.45 J/g·˚C

  7. Specific Heat, C • The amount of energy needed to raise 1˚C (or 1 K) of 1 g (or 1 kg) of a substance • Unit: J/kg∙K; J/g ∙˚C • Unusually high specific heat of ice and water

  8. Sample Problem, Pg 396 • When a 4.25-g sample of solid NH4NO3 dissolves in 60.0 g of water in a calorimeter, the temperature drops form 21.0 °C to 16.9 °C. Calculate ΔH for the solution process. NH4NO3 (s)  NH4+(aq) + NO3‒(aq) ΔH=? (Ans: +19.4 kJ)

  9. Practice Problem 2, Pg 397 • What is the specific heat of nickel if the temperature of a 32.2-g sample of nickel is increased by 3.5 °C when 50. J of heat is added? (Ans = 0.44 J/g·°C)

  10. Practice Problem 1, Pg 397 • When a 13.7-g sample of solid Pb(NO3)2 dissolves in 85.0 g of water in calorimeter, the temperature drops from 23.4°C to 19.7 °C. Calculate ΔH for the solution process. (Ans = 32 kJ) Pb(NO3)2(s)  Pb2+(aq) + 2NO3-(aq) ΔH = ?

  11. Heat Transfer

  12. Heat Needed to Melt a Solid, Hf • No temperature change while a solid is melting • Q = mHf • Hf= heat of fusion = heat needed to melt 1 g or 1 kg of a solid (Ex) Hf of copper = 2.05×105 J/kg Hf of ice = 3.34×105 J/kg

  13. Heat Needed to Boil a Liquid, Hv • No temperature change while a liquid is boiling • Q = mHv • Hv= heat of vaporization = heat needed to boil off 1 g or 1 kg of a liquid (Ex) Hv of copper = 5.07×106 J/kg Hv of water = 2.26×106 J/kg

  14. Example • You need to melt 1.50 kg of snow at 0.0 ˚C and heat it to 70.0 ˚C to make hot cocoa. How much heat will be needed? Hf of ice = 3.34×105 J/kg; Hv of water = 2.26×106 J/kg

  15. Energy Transfer Between Two Objects • Energy transfer (=heat) occurs until two objects reach the same final temperature • One object loses heat; another gains • Qgiven offbyA = ‒ QabsorbedbyB mCA (Tf– Ti, A) = –mCB (Tf– Ti, B)

  16. Example • A calorimeter contains 0.50 kg of water at 15 ˚C. A 0.040-kg block of zinc at 115 ˚C is placed in the water. What is the final temperature of the system? Cwater = 4180 J/Kg∙˚C; Czn = 388 J/Kg∙˚C;

  17. Three Laws of Thermodynamics • First law • Conservation of energy • ∆U = Q + W ∆U = Change in thermal energy (= internal energy) in a system +Q = Heat absorbed by the system ‒Q = Heat given off by the system +W = work done on the system ‒W = work done by the system

  18. Second law • Entropy, S, (randomness, disorder, or chaos) in Universe is always increasing (= spontaneity) • Heat added increases entropy (Ex) Which will add more disorder? a) 10 J heat added to a system at 100 ˚C b) 10 J heat added to a system at -10 ˚C (3) (T must be in K)

  19. Third law: The entropy of a “perfect” crystal is zero. • http://www.allaboutscience.org/common/printable-third-law-of-thermodynamics-faq.htm

  20. Total Q Calculations

More Related