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jess1833 · Aug 11, 2011, 07:54 PM

1. How many grams of liquid sodium (minimum) are needed to absorb 8.40 MJ of energy (in the form of heat) if the temperature of the sodium is not to increase by more than 10*C? Use Cp = 30.8 J/(K * mol) for Na(l) at 500 K

2. An 80.0-gram sample of gas was heated from 25*C to 225*C. During the process, 346 J of work was done by the system and its internal energy increased by 9415 J. What is the specific heat of gas?

3. At constant volume, the heat of combustion of a particular compound is -3931.o kJ/mol. When 1.485 g of this compound (molar mass = 120.24 g/mol) was burned in a bomb calorimeter, the temperature of the calorimeter (including its contents) rose by 3.357*C. What is the heat capacity (calorimeter constant) of the calorimeter? (in kJ/*C)

Unknown008 · Aug 12, 2011, 08:16 AM

1. Use Q = mcT ?

2. Use the formula:

$\Delta U = \Delta Q + \Delta W$

And $\Delta Q = mc\theta$

Bear in mind that the work done is negative when the gas is doing work.

3. Find the total energy that the compound released by using the heat of combustion, the molar mass and the mass of the given sample.

From that and applying your thermodynamics equation,

$\Delta U = \Delta Q + \Delta W$

But

$\Delta U = 0$

$\Delta U = \Delta U_{system} + \Delta U_{surroundings}$

So you get $\Delta U_{system} = - \Delta U_{surroundings} = C_v \Delta T$

Can you try it? :)

fundo · Nov 11, 2012, 01:11 PM

.47