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Heat of Reaction Experiment 23

Heat of Reaction Experiment 23. Purpose: To observe and measure heat transfer between liquids from a chemical reaction. Calorimetry – The measurement of heat effects in chemical and physical processes. Specific Heat.

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Heat of Reaction Experiment 23

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  1. Heat of Reaction Experiment 23

  2. Purpose: To observe and measure heat transfer between liquids from a chemical reaction. Calorimetry – The measurement of heat effects in chemical and physical processes.

  3. Specific Heat • Specific Heat– The amount of heat required to raise 1 gram of substance 1 C. • Note: Specific heat of water = 1 calorie /(gram  C) • The device used to measure the transfer of heat is the calorimeter.

  4. Three types of Heat • Conduction – When two bodies are next to each other. No mixing of liquids or material. Two cans of soda sitting next to each other (one is hot and one is cold). • Convection – an exchange of molecules; both cans of soda are poured into one large glass. The colder liquid absorbs heat while the warmer liquid releases it. Also a pot of boiling water. • Radiation – light from the sun is absorbed and heats an object. A sandy beach in the summer.

  5. Q = MC(T) • Q = heat flow for hot (QH) or cold (QC) liquid • M = mass of water (grams) • C = specific heat of water (1 cal/g C) • T = (Tf –Ti) (in C)

  6. Qh = 50g  1 cal/g C (32 C – 40 C) = - 400 calories “Losing heat” Qc = 50g  1 cal/g C (32 C – 25 C) = 350 cal “Gaining heat” Compute Qhot and Qcold Example # 1 : 50g of hot water at 40 C is mixed with 50 g of cool water at 25 C. After mixing, the final temperature was 32 C. Q = MC(T) T= Tf-Ti

  7. How much heat is absorbed by your calorimeter? Q cal = Heat stolen by calorimeter Q cal = -[Qh + Qc] From the last problem: Qh = - 400 calories Qc = 350 cal Q cal = -[Qh + Qc] Q cal = -[- 400 cal + 350 cal] = +50 calories Q cal = +50 calories stolen by calorimeter • Each calorimeter absorbs a different amount of heat.Use the same calorimeter for part #2.

  8. Part One: • Determine the amount of heat that your calorimeter absorbs. • Calculate Hc • The calorimeter absorbed heat that should have been gained by the cold water. • We must calculate Hc (Heat Capacity):this will be a correction factor for part #2. • Hc = the calories absorbed by the calorimeter/ the change in temp for the cold water. From my trial: Q cal = + 50 calories so Hc = 50 cal / 7.0 OC = 7.1cal/ OC

  9. Part Two: • Determine the amount of energy released during a chemical reaction. • HCl + NaOH  NaCl + H2O + Heat Energy (Higher in energy) (Lower in energy) • Note: This reaction is exothermic thus energy is released. Determine the heat released in a chemical reaction when 20.0g of HCl at 22 C was added to 20.0g of NaOH at 22 C. The final temperature was 28 C. Same calorimeter as in Part I; use Hc from Part I. 7.1cal/ OC

  10. QRx = -[Q Observed+ HcΔT] Q Observed = what we recorded during the reaction. Q Rx = what is actually released during the reaction QObserved=McΔT So we have: Q Rx = -[McΔT + HcΔT] ΔT HC ΔT

  11. We can determine the amount of heat absorbed by the environment by using: QRx = - QSurr If: QRx=-282 cal -282cal = - Q Surr Q Observed = what we recorded during the reaction. Qsurr =what is absorbed in the environment Q Rx = what is released by the reaction

  12. Today in Lab • Part # 1 • Determine Hc for your calorimeter • Add 80 ml of water @ room temp to your cal. • Heat water 80g of water to 60OC • Once at temperature remove from heat. • Record initial temps for both the hot and cold water. In tables 23-2 & 3

  13. Once at 60OC. • Start the timer, and record your initial temperature in table 23-1. • Continue to record the temp of your hot water every 30 seconds for 2.5 minutes. • At 150 sec (2.5 min) pour the hot water into the calorimeter and continue to record the temperatures. • Do two trials, and use the better of the two for part #2. • Graph the data that you use in part #2.

  14. Part # 2 Determine the amount of heat that is generated from the reaction. • Add 50mL. of HCl into the calorimeter. • Pour 50mL. of NaOH into a beaker. • Record the initial temps. of both and record data in table 23-5 • Pour the NaOH into the calorimeter, turn on the timer, mix, and record temps.

  15. Due next week • Your calculations for each trial in part #1, data and calculations from part # 2. • Show all work for full credit. • Two graphs one for each part. • A graphs done on graph paper will be accepted this time.

  16. 23-2 23-1 23-3

  17. 23-4 23-5

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