CHEM151Take-home Q12 Key

Chemistry (MasteringChemistry Series)

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Take Home Quiz # 12 (DUE Wednesday December 10 th , 2008) Name KEY Date Score 1) Explain why heat (q) and enthalpy ( H) have negative values when leaving a system and positive values when entering a system. (1 point) Heat leaving system: f<i Æ f – i = ( ) value Heat entering a system: f>i Æ f – i = (+) value 2) A 27.7 g sample of ethylene glycol, car radiator coolant, loses 688 J of heat. What is the initial temperature of the ethylene glycol if the final temperature is 32.5 ºC (specific heat, c, of ethylene glycol = 2.42 J/g K?) (Hint: watch your signs) (2 points) Loses 688 J Æ q = 688 J Units of specific heat (J/g K) Æ need to covert temp. (32.5°C + 273 = 305.5 K ݍൌ݉ݏ∆ܶൌ݉ݏ൫ܶ െܶ െ688ܬ ൌ 27.7݃ · 2.42 ௚௞ ሺ305.5ܭ െ ܶ െ688ܬ 67.0 ൌ 305.5ܭ െ ܶ െ10.3ܭ െ 305.5ܭ ൌ െܶ ૜૚૟ࡷ ൌ ࢀ ൌ 316ܭ െ 273 ൌ ૝૜°࡯ 3) A 30.5 g sample of copper at 93.0°C is placed into 50.0 g of water at 22.0°C. Both the copper
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CHEM151Take-home Q12 Key - Name

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