# Find the latent heat of vaporization

• mibson
In summary: Thanks again for the help!It sounds like you are not sure what the correct answer is either. So I will give you a few suggestions and you can choose which one you think is correct. 1. If the answer is "Hg - Hf = Hfg", then the latent heat of vaporization is 2373.06 kJ/kg. 2. If the answer is "Cp * dT", then the latent heat of vaporization is 1.058252 J/g.
mibson
Simple Q - Latent Heat of vaporization H20 @15 C and 115 C

sorry , I have reposted in the homework help section...

I am not good a math and physics and I am taking a intro Food Engineering course. My question on my assignment states " Find the latent heat of vaporization for water at 15 °C and 115 °C"

I know it is very simple but it seems like there is info left out for us to assume? or perhaps this is just found looking in tables. I am just not sure the correct answer.

Thanks for any help!

Mibson

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## Homework Statement

I am not good a math and physics and I am taking a intro Food Engineering course. My question on my assignment states " Find the latent heat of vaporization for water at 15 °C and 115 °C"

I know it is very simple but it seems like there is info left out for us to assume? or perhaps this is just found looking in tables. I am just not sure the correct answer. I have search online and keep finding the equation Q = mL

Thanks for any help!

Mibson

## Homework Equations

I know the equations in my notes but I don't think this even requires a calculation.

The molecular formula of water is H20 so perhaps I need the molecular mass of H and O thus 1.00794 and 2x(15.9994) = 33.00674 ; is this g/mol (its been 10 years since I took chemistry)

Latent Heat of Vaporization = Hg - Hf = Hfg (this is in my notes)

What I don't understand is that I thought the Latent Heat of Vaporization is for when a phase change is happening and I thought phase changes occur at ~0C and ~100C

Also in my notes it says Hg - Hf = Hfg = 2373.06 kJ/kg,

## The Attempt at a Solution

I have read my notes 4 times and been doing this simple question for over two hours. It seems to me like the prof has not stated things we must assume to answer the question.

Perhaps it is just 2272 J/g?

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Well there really isn't much to assume. Things you know is the molecular formula of water, and you can easily find it's specific heat & heat of vaporization.

What formula do you think you will need to use in order to calculate it's latent heat of vaporization?

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The molecular formula of water is H20 so perhaps I need the molecular mass of H and O thus 1.00794 and 2x(15.9994) = 33.00674 ; is this g/mol (its been 10 years since I took chemistry)

Latent Heat of Vaporization = Hg - Hf = Hfg (this is in my notes)

What I don't understand is that I thought the Latent Heat of Vaporization is for when a phase change is happening and I thought phase changes occur at ~0C and ~100C

Also in my notes it says Hg - Hf = Hfg = 2373.06 kJ/kg,

Thanks for the help!

Last edited:
It sounds like this may be something you need a steam table for (hg, hf, and hfg are out of a steam table). Do you have one?

IIRC, you can also use Hfg and add to it the h required to change the temperature from 15->100C (for the first part...). This would be based on Cp * dT (specific heat times temperature difference).

At some temperatures and pressures, water can exist in more than one phase. If it is evaporationg, it is changing from a liquid to a gas, and as you know air at normal everyday temperatures is capable of holding a certain amount of water vapor.

I have a steam table but don't undertand it completely. I have to chose one of two tabs : staturated OR superheated/subcooled ; The only one where temperature is the only input is the saturated one but I don't see how there would only be steam at 15C perhaps at 115C it will all be steam. Basically using the "staturated" tab does not make a lot of sense to me as I don't see how the h2o at 15C would be saturated steam...

## 1. What is the definition of latent heat of vaporization?

The latent heat of vaporization is the amount of energy required to convert a substance from its liquid state to its gaseous state at a constant temperature and pressure.

## 2. How is the latent heat of vaporization measured?

The latent heat of vaporization can be measured experimentally by heating a substance at a constant pressure and measuring the amount of energy required to vaporize it completely.

## 3. What factors can affect the latent heat of vaporization?

The latent heat of vaporization can be affected by factors such as temperature, pressure, and the substance's molecular structure.

## 4. What is the difference between latent heat of vaporization and latent heat of fusion?

The latent heat of vaporization is the amount of energy required to vaporize a substance, while the latent heat of fusion is the amount of energy required to melt a substance. Both involve a change in the substance's state, but at different temperatures and pressures.

## 5. Why is knowing the latent heat of vaporization important?

Knowing the latent heat of vaporization is important in various industries, such as in refrigeration and power generation, as it determines the amount of energy needed to change a substance's state and can help optimize processes and equipment.

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