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NaCl has a (delta)Hfus = 30.2 kJ/mol and a (delta)Hvap = 171 kJ/mol. What mass of NaCl releases 452 kJ of heat as it changes into a gas? Use q=n(delta)H
2.64 g
22.1 g
155 g
875 g

Respuesta :

Yna9141
The equation that is necessary in order to solve this item, is already written in the question as,
     q = n(delta)H

However it was not defined which among the given heat constants is to be used. The situation given in this item is the changing of the phase from liquid to gas. Therefore, this involves the heat of vaporization (delta)Hvap.

The amount of NaCl is calculated through the equation,
   n = q/ (delta Hvap)

Substituting the known values,
   n = (452 kJ) / (171 kJ/mol) 
  n = 2.64 mol

Then, we multiply the obtained value by the molar mass of NaCl, 58.44 g/mol.

   m = (2.64 mol)(58.44 g/mol)
   m = 154.28 g

ANSWER: 154.28 g
CintiaSalazar

Taking into account the definition of calorimetry and latent heat, the correct answer is the first option: 2.64 g of NaCl releases 452 kJ of heat as it changes into a gas.

Calorimetry

Calorimetry is the measurement and calculation of the amounts of heat exchanged by a body or a system.

Latent heat

Latent heat is defined as the energy required by a quantity of substance to change state.

When this change consists of changing from a solid to a liquid phase, it is called heat of fusion and when the change occurs from a liquid to a gaseous state, it is called heat of vaporization.

The heat Q that is necessary to provide for a mass m of a certain substance to change phase is equal to

Q = m×L

where:

  • L is called the latent heat of the substance and depends on the type of phase change.
  • m is the amount of substance that you have.

Mass of NaCl releases

In this case, you know:

  • Q= 452 kJ
  • m=?
  • L= 171 [tex]\frac{kJ}{mol}[/tex]because the change occurs from a liquid to a gaseous state.

Replacing in the definition of latent heat:

452 kJ= m× 171 [tex]\frac{kJ}{mol}[/tex]

Solving:

452 kJ÷ 171 [tex]\frac{kJ}{mol}[/tex]= m

2.64 g= m

Finally, the correct answer is the first option: 2.64 g of NaCl releases 452 kJ of heat as it changes into a gas.

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