1. A 150-W heater was placed in 1.00 kg of methanol and turned on for exactly 1

Question

1. A 150-W heater was placed in 1.00 kg of methanol and turned on for exactly 1 min. The temperature increased by 3.54 C. Assuming that all the heat is absorbed by the methanol, calculate the molar heat capacity of methanol. 2. Exactly 10 kJ of energy was absorbed by 1 mol of Cl2(g) at 298 K. What is the final temperature of the Cl2(g)? The heat capacity of C12(g) is 25.635J K- 1 mol-1 3. Determine the specific heat and the molar heat capacity of liquid water at 25 C and 1 atm given that exactly 100 cal produces a temperature increase of 1.00172 K in exactly 100 g of water.

Explanation / Answer

1) heat produced = Power X time in seconds = 150 X 60 Joules = 9000 Joules

The increased in temperature = 3.54

Mass of methanol = 1000grams

Heat given = Heat absorbed by methanol

9000 = Mass X specific heat of methanol x increase in temperature

9000 = 1000 X specifc heat X 3.54

Specific heat = 2.54 J / 0C gram

molecular weight of methanol = 32 g / mol

So molar heat capacity = specific heat X 32 = 2.54 X 32 = 81.28 J / 0C mole

2) Heat absorbed = Moles X heat capcity X Change in temperature

10000 = 1 X 25.635 X Change in temperature

Change in temperature = 390.09 Kelving

Initial temperature = 298 K

so final temperature = 298 X 390.09 = 688.09 K

3) Heat = Mass X change in temperture X specific heat of water

100 = 100 X 1.00172 X Specific heat of water

specific heat of water = 0.998 Cal / K grams

Molar heat capacity = specific heat of water X molecular weight = 0.998 X 18 = 17.964 Cal / K mol

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