HW 8-Temperature_Heat

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CUNY Borough of Manhattan Community College *

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ACC 231

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Chemistry

Date

Jan 9, 2024

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docx

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Homework 09 - Temperature and Heat (Ch. 10) - PHY 110 Due Date: Name__________________ . Score: ______ 1. Absolute zero is the temperature ( ) on the coldest day recorded at Nome, Alaska. (x ) at which an ideal gas would exert zero pressure. ( ) of the boiling point of liquid helium. ( ) of the freezing point of mercury. 2. Fill in the following temperatures in Celsius and Kelvin Absolute zero freezing point of water boiling point of water ° C _______ _______ _______ ° K _______ _______ _______ Absolute zero = -273.15oC = 0 K Freezing point = 0oC = 273.15 K Boiling point = 100oC = 373.15 K 3. The temperature of 500 g of water is to be raised from 10 °C to 40 °C. The energy needed to do this is about ( ) 5 x10 3 cal Show calculation: (x ) 1.5 x10 4 cal E= 500 x 1 cal/gooc x 30. c ( ) 2 x10 4 cal E=1.5 x 10^4 cal ( ) 4 x10 4 cal 4. If 45 calories of heat energy are added to 5 gram of water, the temperature of the water will ( ) decrease by __°C. (x ) increase by _9_°C. Show calculation: 45/5x1 5. The temperature of a 50 g sample of aluminum is raised from 20 °C to 90 °C when 770 cal of heat is added. The specific heat capacity of the aluminum is Show calculation: ( ) 0.11 cal/g °C c= 770/50 x 70 = 0.22 ( ) 15.4 cal/g °C ( x) 0.22 cal/g °C ( ) 0.91 cal/g °C. 6. Four samples of steel, lead, alcohol and glass all have the same mass and are all initially at 20 °C. After 100 calories of heat is added to each sample, the final temperatures are 38.2 °C for the steel, 85.6 °C for the lead, 23.4 °C for the alcohol, and 30 °C for the glass. Which of these four materials has the largest specific heat capacity? Show calculation: ( ) The steel ( ) The lead ( ) The alcohol ( ) The glass 7. During a phase change the ___________________ of a system will remain constant as heat is added. 8. A mixture consists of 60 g of ice and 40 g of liquid water, both at 0°C. The amount of heat that must be added to melt all of the ice is about (L f =80 cal/g) Show calculation: ( ) 3200 cal ( ) 4000 cal ( ) 4800 cal

( ) 8000 cal

9. An ice cube of mass 100 g and at 0°C is dropped into a Styrofoam cup containing 200 g of water at 25°C. Calculate how much heat is available by cooling the water to 0°C and how much heat is required to melt the ice. L f =80 cal/g; c w = 1.0 cal/g °C Show calculation: Available Heat: Q available = ______cal. Required heat: Q required = ______cal Will all the ice melt? _____ 10. A certain amount of heat is transferred to a system, and the system performs some work on its surroundings. The amount of work done is less than the heat added. Thus ( ) the internal energy of the system increased. ( ) the internal energy of the system decreased. ( ) there has been a violation of the principle of conservation of energy. ( ) there must have been a phase change. 11. The volume of an ideal gas is increased from 1 m 3 to 3 m 3 at a constant pressure of 1000 Pa How much work is done by the gas in the expansion? Show calculation: W= _________ J If no heat has been added or removed, what is the change in internal energy of the gas?  U = ________ J 12. Work of 1500 J is done on an ideal gas, but the internal energy raises only 800 J. What is the amount and direction of the heat flow into or out of the gas? Hint: Convert J to cal ! Show calculation Q = ______ cal 13. If 500 cal of heat is added to a gas, and the gas expands doing 500 J of work on its surroundings, what is the change in the internal energy of the gas? Hint: Convert cal to J ! Show calculation:  U = ______ J 14. Heat is added to an ideal gas and the gas expands. In such a process the temperature ( ) must always increase. ( ) will remain the same if the work done equals the heat added. ( ) will remain the same if work done is less than the heat added. ( ) will remain the same if the work done exceeds the heat added. 15. Which of the three processes of heat flow is most effective for: (a) A hot body in vacuum , e.g. a star like the the sun in space ____________ (b) A hot liquid , e.g. the liquid outer iron-nickel core of the Earth ____________ (c) A hot solid, e.g. the solid inner iron-nickel core of the Earth ____________ 16. * Calculate the amount of heat to be added to warm 150 g of ice from -10°C to produce steam at 110°C? (2 pts) Ice: c ice = 0.5 cal/g·°C, L f =80 cal/g; Water c w =1.0 cal/g·°C; Steam c steam = 0.5 cal/g·°C, L v =540 cal/g ( ) 12, 000 cal Show calculation: ( ) 81 kcal ( ) 109.5 kcal ( ) other ________

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