Specific heat at constant pressure formula help

In summary: Cp is used because it is a measure of how enthalpy changes with temperature at constant pressure. In this problem, the pressure is changing, but the temperature is constant, so we can use Cp to calculate the change in enthalpy.
  • #1
yecko
Gold Member
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15

Homework Statement


f2vSXtq.png

https://i.imgur.com/f2vSXtq.png

Homework Equations


Kjy1Tzh.png

https://i.imgur.com/Kjy1Tzh.png

The Attempt at a Solution


In this question, the pressure is different at different point, in other words it is not constant throughout the system. Why the solution use c(p) (or "enthalpy" h which specified for constant pressure system) as part of the formula used?

Thank you very much!
 
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  • #2
yecko said:

Homework Statement


View attachment 211514
https://i.imgur.com/f2vSXtq.png

Homework Equations


View attachment 211515
https://i.imgur.com/Kjy1Tzh.png

The Attempt at a Solution


In this question, the pressure is different at different point, in other words it is not constant throughout the system. Why the solution use c(p) (or "enthalpy" h which specified for constant pressure system) as part of the formula used?

Thank you very much!
For an ideal gas, enthalpy is independent of pressure. Doesn't the open system version of the first law require you to use enthalpy?
 
  • #3
Chestermiller said:
For an ideal gas, enthalpy is independent of pressure. Doesn't the open system version of the first law require you to use enthalpy?
Is that imply enthalpy is used just because the first law of thermodynamics is applicable?
And using Cp is not contradict to the situation of pressure changed, but rather Cp is used because it can trace out the enthalpy?
Thank you very much!
 
  • #4
yecko said:
Is that imply enthalpy is used just because the first law of thermodynamics is applicable?

Yes. The open system version of the first law tells us that, for your problem the change in enthalpy is equal to the change in kinetic energy.
And using Cp is not contradict to the situation of pressure changed, but rather Cp is used because it can trace out the enthalpy?
Thank you very much!
Yes.
 

FAQ: Specific heat at constant pressure formula help

1. What is the formula for calculating specific heat at constant pressure?

The formula for calculating specific heat at constant pressure is Q = m x Cp x ΔT, where Q is the amount of heat transferred, m is the mass of the substance, Cp is the specific heat at constant pressure, and ΔT is the change in temperature.

2. How is specific heat at constant pressure different from specific heat at constant volume?

Specific heat at constant pressure (Cp) is the amount of heat required to raise the temperature of a substance by 1 degree Celsius at constant pressure. Specific heat at constant volume (Cv) is the amount of heat required to raise the temperature of a substance by 1 degree Celsius at constant volume. Cp is typically higher than Cv because at constant pressure, the substance is allowed to expand and do work, while at constant volume, no work is done.

3. What are the units for specific heat at constant pressure?

The units for specific heat at constant pressure are joules per kilogram per degree Celsius (J/kg°C) in the SI system and calories per gram per degree Celsius (cal/g°C) in the CGS system.

4. How does specific heat at constant pressure vary for different substances?

The specific heat at constant pressure varies for different substances due to differences in their molecular structure and composition. For example, substances with stronger intermolecular forces tend to have higher specific heat at constant pressure because more energy is required to break these bonds and raise the temperature.

5. What is the significance of specific heat at constant pressure in thermodynamics?

Specific heat at constant pressure is an important factor in thermodynamics as it helps to determine the amount of heat required to increase the temperature of a substance. It is also used to calculate the heat capacity of a substance, which is necessary for determining the amount of energy needed for various processes such as heating and cooling. Additionally, specific heat at constant pressure is used in the calculation of enthalpy, a thermodynamic quantity that measures the total energy of a system.

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