calorimeter problem

[inaccensa]

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20 grams of NaCl is poured into a coffee cup calorimeter
containing 250 ml of water. If the temperature inside the
calorimeter drops 1°C by the time the NaCI is totally
dissolved, what is the heat of solution for NaCl and
water? (specific heat of water is 4.18 J/gC.)

This system is at constant pressure, change in enthalpy = Q

Q =mc*change in temp

How do we get the mass?
20gms NaCl * 1 mole NaCl * 1000ml * 1L = 13.33moles NaCl/ Kg
58 gms NaCl 250ml water 1L 1Kg

 

[Isoprop]

20 grams of NaCl is poured into a coffee cup calorimeter
containing 250 ml of water. If the temperature inside the
calorimeter drops 1°C by the time the NaCI is totally
dissolved, what is the heat of solution for NaCl and
water? (specific heat of water is 4.18 J/gC.)

This system is at constant pressure, change in enthalpy = Q

Q =mc*change in temp

How do we get the mass?
20gms NaCl * 1 mole NaCl * 1000ml * 1L = 13.33moles NaCl/ Kg
58 gms NaCl 250ml water 1L 1Kg

you are measuring the change in temperature of the water. so you are interested in the mass of the water. the density of water is 1 g/mL.

 

[Tokspor]

you are measuring the change in temperature of the water. so you are interested in the mass of the water. the density of water is 1 g/mL.

Do you need to add the mass of NaCl to that of water in q = m*c*delta T?

 

[ChemEngSoonMD]

Do you need to add the mass of NaCl to that of water in q = m*c*delta T?

No, because:

1. MCAT tests easy questions.
2. They didn't give you the specific heat of NaCl, so why would you use the specific heat of water a with the negligible mass of the NaCl?