# How to Calculate Heat of Vaporization Given Pressure And Temperature? ##### Joseph Hebert
Owner at - HVAC Buster

Joseph is an HVAC technician and a hobbyist blogger. He’s been working as an HVAC technician for almost 13 years, and he started blogging just...Read more

To calculate the heat of vaporization, you need to know the pressure and temperature at which the material boils. This can be found in a variety of ways, but the most accurate way is to use an instrument called a manometer. With this tool, you can take readings of both the temperature and pressure at the same time.

• To calculate the heat of vaporization, you will need to know both the pressure and temperature at which the vaporization occurs
• Use the ideal gas law to find the number of moles of gas present in the sample
• Convert the number of moles to grams using the molar mass of the gas
• Find the enthalpy of vaporization from a table or graph, using the pressure and temperature that you found in Step 1
• Multiply the enthalpy of vaporization by the number of grams calculated in Step 3 to find the heat of vaporization for your sample

## Clausius-Clapeyron Equation

In 1834, two physicists independently came up with an equation that would later become known as the Clausius-Clapeyron Equation. The equation relates the pressure of a gas to its temperature and is derived from the First Law of Thermodynamics. The Clausius-Clapeyron Equation can be used to find the boiling point of a substance at a given pressure.

It can also be used to find the critical point of a substance, which is the point at which it can no longer exist as a liquid or gas. To use the Clausius-Clapeyron Equation, you need to know three things: the heat of vaporization (ΔHvap), the molar mass of the substance (M), and either the boiling point (Tb) or critical point (Tc) temperature. With this information, you can plug values into the following equation:

ln(P2/P1) = – ΔHvap/(R*T2–T1) + ln(M2/M1)  where P is pressure, T is temperature, R is universal gas constant, and M is molar mass. This equation may look daunting, but it’s actually not too difficult to use once you get familiar with it. Let’s say you want to find out what happens to water when it reaches its critical point.

In this case, we’ll set P1 = 1 atmosphere (atm), T1 = 293K (20°C or 68°F), P2 = 2atm, and T2 = 705K (430°C or 800°F). Plugging these values into our equation gives us: ln(2/1) = – 44000 J/mol*K *(705K – 293K)/(8.31446J/mol*K * 705K *293K ) + ln(18g/mol / 16g/mol)= 3.93  where J is joules and g is grams mol−1 .

We can see that as water approaches its critical point, its molecules start moving faster and faster until they reach a state where they can no longer be distinguished from each other.

## How to Calculate Heat of Vaporization of Water

The heat of vaporization is the energy required to convert a liquid into a gas. The heat of vaporization of water is the highest of any common substance and is essential for life on Earth. To calculate the heat of vaporization, we need to know the enthalpy of vaporization and the entropy of vaporization.

The enthalpy of vaporization is the change in enthalpy when one mole of liquid water turns into one mole of steam at 100°C and 1 atmosphere pressure. The entropy of vaporization is the change in entropy when one mole of liquid water turns into one mole of steam at 100°C and 1 atmosphere pressure. The heat of vaporization can be calculated using the equation:

heatofvaporization = enthalpyofvaporization + entropyofvaporization For water, the enthalpyofvaporization is 2,260 kJ/mol and the entropyofvaporizaton is 1,040 J/K•mol. Therefore, the heatofvaporizaton for water is 2,260 kJ/mol + 1,040 J/K•mol = 3,300 kJ/mol.

## How to Calculate Heat of Vaporization Given Temperature

In order to calculate the heat of vaporization, you need to know two things: the boiling point of the liquid and the enthalpy of vaporization. The boiling point is the temperature at which the liquid boils and turns into a gas. The enthalpy of vaporization is the amount of energy that is required to turn one mole of a liquid into a gas.

With these two pieces of information, you can use the following equation: heat of vaporization = (boiling point – temperature) x enthalpy of vaporization Let’s say we want to calculate the heat of vaporization for water.

We know that water boils at 100 degrees Celsius and that its enthalpy of vaporization is 40 kJ/mol. Plugging these values into our equation, we get:

## How to Find Heat of Vaporization from a Graph

It can be difficult to find the heat of vaporization from a graph. However, there are a few steps that can make it easier. First, identify the boiling point on the graph.

This is the temperature at which the liquid changes to a gas. Next, find the temperature at which the liquid starts to boil. This is called the saturation temperature.

Finally, subtract the saturation temperature from the boiling point to find the heat of vaporization.

## Molar Heat of Vaporization of Water

“The molar heat of vaporization (ΔHvap) of water is the amount of heat required to turn one mole of liquid water into vapor at a constant temperature. The value is usually given for a particular temperature, such as 25 °C or 100 °C. The lower the temperature, the higher the ΔHvap.

The average value of ΔHvap for water over a range of temperatures can be found in various sources. For example, according to CRC Handbook of Chemistry and Physics, 91 J/mol is the value at 25 °C, while NIST Chemistry WebBook reports 118 J/mol at 25 °C.

## How Do You Calculate Heat of Vaporization?

In order to calculate the heat of vaporization, you need to know the enthalpy of vaporization and the molar mass of the substance. The enthalpy of vaporization is the amount of heat that is required to change one mole of a liquid into a gas. The molar mass is the amount of grams that are in one mole of a substance.

To calculate the heat of vaporization, you divide the enthalpy by the molar mass.

## How Do You Calculate the Enthalpy of Vaporization Given Vapor Pressure?

In order to calculate the enthalpy of vaporization, you need to know the vapor pressure of the substance in question. This can be found using the Clausius-Clapeyron equation: ln(P2/P1) = (ΔHvap/R)(1/T2 – 1/T1)

Where P2 is the vapor pressure at temperature T2, and P1 is the vapor pressure at temperature T1. R is the gas constant, and ΔHvap is the change in enthalpy during vaporization. You can rearrange this equation to solve for ΔHvap:

## What Formula is Q Mc ∆ T?

In physics, the heat capacity ratio or adiabatic index is the ratio of the heat capacity at constant pressure to heat capacity at constant volume. It is also known as the isentropic expansion factor and is denoted by γ for an ideal gas. For a diatomic gas, such as nitrogen or oxygen, γ = 7/5.

The heat capacity ratios of some other common gases are shown in the table below. The heat capacity ratio is related to the compressibility factor Z by γ = Z(1 + β)

where β = (PV)/(RT) is the second virial coefficient. For an ideal gas, β = 0 and γ = Z. The compressibility factor deviates from unity for real gases due to intermolecular forces, which cause the molecules to occupy less space than they would in an ideal gas. As a result, γ < Z for real gases.

The heat capacity ratios of some common liquids and solids are also shown in the table below. For liquids and solids, intermolecular forces are much stronger than they are for gases, so their compressibility factors are closer to unity and their heat capacity ratios are closer to Z than they are for gases.

## How Does Heat of Vaporization Change With Pressure?

The heat of vaporization is the amount of energy required to change a substance from a liquid to a gas. The higher the pressure, the higher the heat of vaporization. This is because it takes more energy to overcome the intermolecular attractions between molecules in a liquid when there is more pressure on them.

## Conclusion

The heat of vaporization is the amount of heat that a liquid must absorb in order to change into a gas. The higher the pressure, the higher the heat of vaporization will be. The temperature also has an effect on the heat of vaporization.

At lower temperatures, the molecules in a liquid are more closely packed together, and it takes more energy to separate them. Joseph is an HVAC technician and a hobbyist blogger. He’s been working as an HVAC technician for almost 13 years, and he started blogging just a couple of years ago. Joseph loves to talk about HVAC devices, their uses, maintenance, installation, fixing, and different problems people face with their HVAC devices. He created Hvacbuster to share his knowledge and decade of experiences with people who don’t have any prior knowledge about these devices.