Module Eleven Lesson Three Activity Answer Key

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Chemistry

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Nov 24, 2024

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Google Doc Access Directions: ● Please click on File in the upper left corner. ● If you are working on a Chromebook or Google Docs, choose the Make a copy option and save a copy of the document to your Google Drive. ● If not, choose the Download as option and then the Microsoft Word (.docx) option to download an editable copy of the document to your computer. Heating Curve Problems 1. Calculate the amount of energy required to heat 30 g of water from - 45 o C to steam at 190 o C. a) Which phases and transitions are required? Liquid water to steam (gaseous) (evaporation) b) Calculate each Q and Qtotal. Steps Needed: heat for liquid water from 45°C to 100°C + heat needed to vaporize 30 grams of water + heat needed to heat gaseous water from 100°C to 190°C Step 1: Calculate heat absorbed to heat liquid water from 45°C to 100°C: Q = mc Δ T Q = (30 g) (4.18 J/g°C) (100° - 45°C) Q = (30 g) (4.18 J/g°C) (55°C) Q = 6,897 J Step 2: Calculate heat needed to vaporize 30 grams of water Qv = mHv Qv = (30 g) (2260 J/ g) Qv = 67,800 J Step 3: Calculate heat needed to heat gaseous water from 100°C to 190°C Q = mc Δ T Q = (30 g) (2.02 J/g*°C)(190°C-100°C) Q = (30 g) (2.02 J/g*°C) (90°C) Q = 5,454 J Step 4: Add the heats from Steps 1, 2, and 3 together Qtotal = Qstep1 + Qstep2 + Qstep3 Qtotal = 6,897 J + 67,800 J + 5,454 J Qtoal = 80,151 J Q=mcΔT Q f = mH f Q v = mH v c solid = 2.05 J/g o C H f = 334 J/g H v = 2260 J/g c liquid = 4.18 J/g o C C gas = 2.02 J/g o C 2. Calculate the amount of energy required to heat 400 g of ice from -55 o C to steam at 600 o C. a) Calculate each Q and Qtotal. Q=mcΔT Q f = mH f Q v = mH v c solid = 2.05 J/g o C H f = 334 J/g H v = 2260 J/g c liquid = 4.18 J/g o C

C gas = 2.02 J/g o C Steps Needed: heat for solid water from -55°C to 0°C +heat needed to melt 400 g water + heat for liquid water from 0°C to 100°C + heat needed to vaporize 400 grams of water + heat needed to heat gaseous water from 100°C to 600°C Step 1: Calculate heat absorbed to heat solid water from -55°C to 0°C: Q = mc Δ T Q = (400 g) (2.05 J/g°C) (0° - (-55°C)) Q = (400 g) (2.05 J/g°C) (55°C) Q = 45,100 J Step 2: Calculate heat needed to melt 400 grams of water Qf = mHf Qf = (400 g) (334 J/ g) Qf = 133,600 J Step 3: Calculate heat needed to heat gaseous water from 0°C to 100°C Q = mc Δ T Q = (400 g) (4.18 J/g*°C)(100°C-0°C) Q = (400 g) (4.18 J/g*°C) (100°C) Q = 167,200 J Step 4: Calculate the heat needed to vaporize 400 grams Qv= mHv Qv = (400 g) (2260 J/ g) Qf = 904,000 J Step 5: Calculate heat needed to heat gaseous water from 100°C to 600°C Q = mc Δ T Q = (400 g) (2.02 J/g*°C)(600°C-100°C) Q = (400 g) (2.02 J/g*°C) (500°C) Q = 404,000 J Step Add the heats from Steps 1, 2, and 3 together Qtotal = Qstep1 + Qstep2 + Qstep3+Qstep4+Qstep5 Qtotal = 45,100 + 133,600 + 167,200 + 904,00 + 404,000 Qtotal = 1, 653, 900 J 3. When a substance undergoes a phase change from a gas to a liquid, the temperature of that substance [A] decreases [B] stays the same [C] increases [D] may increase or decrease depending on the liquid [E] none of these B – during a phase change, the temperature does NOT change

4. The heating/cooling curve of chloroform is shown below. What is the heat of fusion of chloroform? [A] -63.6 °C [B] 61.7 °C [C] 8.80 kJ/mol [D] 31.4 kJ/mol [E] none of these Correct answer is “C.” Heat of fusion occurs when a substance changes from a solid to a liquid. This represents the first flat part of the graph that shows 8.80 kJ / mol. 5. Given the phase diagram for water state what phase(s) of water is/are present at each of the following temperature-pressure conditions: a) at any point on curve BO Segment BO is the boundary between solid and gas. These are the phases present. b) at any point on curve OA Segment OA is the boundary between liquid and gas. These are the phases present. c) at any point on curve OC Segment OC is the boundary between solid and liquid. These are the phases present. d) at point O Point O represents the triple point – this means that all three phases (solid, liquid, and gas) are present.

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