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Thermochemistry 4

Thermochemistry 4. Boon Chemistry March 3 & 4, 2014. Catalyst. (1) What formula would you use to calculate the heat needed to increase the temperature of the ice from 200 K to 273 K? (2) What formula would you use to calculate the heat needed to melt the ice?. Objectives

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Thermochemistry 4

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  1. Thermochemistry 4 Boon Chemistry March 3 & 4, 2014

  2. Catalyst (1) What formula would you use to calculate the heat needed to increase the temperature of the ice from 200 K to 273 K? (2) What formula would you use to calculate the heat needed to melt the ice? • Objectives • I can solve for the total heat transferred to heat or cool a sample through a phase change. • Agenda • Catalyst • Multi-Step Thermochemistry Problems • PracticeCalculations • Phase Change Diagram Project • Exit Slip

  3. Exothermic vs. Endothermic Mini-Investigation • For each demonstration or video answer the following questions: • Is the process a chemical or physical change? Why? • Is the process exothermic or endothermic? Why?

  4. Multi-Step Thermochemistry Problems • Today we are calculating the amount of heat transferred to increase or decrease the temperature of a substance and cause a phase change. • We are combining what we learned last week and this week. • Example: How much heat is absorbed when 100 g of water is heated from 365 K to steam at 400 K?

  5. Multi-Step Thermochemistry Problems • Step 1: Break down the problem into “temperature change” and “phase change” steps. • Use the boiling point and melting point as a guide. • Step 2: Solve the steps separately. • Use q=mcΔT for temperature change and q = mΔHt for phase change • Step 3: Add up the answers to get the total heat transferred.

  6. Example: How much heat is absorbed when 100 g of water is heated from 365 K to steam at 400 K? • Step 1: The boiling point of water is 373 K. So, break up the problem in three parts: (a) 365K to 373K, (b) vaporization and (c) 373K to 400K. • Step 2: Set up and solve the problems. Then step 3: add up the answers.

  7. Example 2: How much heat is released when 2500 g of water is cooled from 70 °C to ice at -10°C? • Step 1: The melting point of water is 0°C. So, break up the problem in three parts: (a) 70°C to 0°C, (b) freezing and (c) 0°C to -10 °C. • Step 2: Set up and solve the problems. Then step 3: add up the answers.

  8. Think, Pair, Share • How many steps would you split these problem into? Why? • How much heat is absorbed when 5000 g of water is heated from 275 K to 370 K? • How much heat is absorbed when 10,000 g of ice at 0°C is melted and heated to steam at 150°C?

  9. Work Time • Work quietly at your table to complete the practice problems. • Get a stamp when you finish and check your work. • Work on any thermochemistry worksheets that you have not yet finished. • Work on Parts #1-3 of your Phase Change Diagram Project. • For detailed guides to calculations and unit conversions, see the edmodo page. • Reading and Vocabulary practice activities: Go to edmodo.com for today’s menu of vocabulary and reading activities.

  10. Homework • Due Wed. March 5th: Complete Steps #1-3 of the Phase Change Diagram Project. Show all work for calculations on a separate sheet of paper. • Due Thur/Fri March 6th/7th: read pp. 576-585 and answer questions on pp. 585 #1-7. • Due Wed. March 12th: Phase Change Diagram Project.

  11. Multi-Step Thermochemistry Problems • Step 1: Break down the problem into “temperature change” and “phase change” steps. • Use the boiling point and melting point as a guide. • Step 2: Solve the steps separately. • Use q=mcΔT for temperature change and q = mΔHt for phase change • Step 3: Add up the answers to get the total heat transferred.

  12. Practice 3: A 150 g piece of aluminum foil is heated from 70 °C to 700 °C. The heat of fusion of aluminum is 398 J/g. The melting point of aluminum is 660 °C. Calculate the heat transferred to the aluminum. 70°C to 660 °C Melting 660 °C 660°C to 700°C Q = (m) (c) ΔT Q = (m) ΔH Q = (m) (c) ΔT Q = (150g) (0.897J/g*C) (590C) Q = (150g) (398J/g) Q = (150g) (0.897J/g*C) (40C)

  13. Homework • Due Monday/Tuesday: read pp. 576-585 and answer questions on pp. 585 #1-13.

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