Heat calculation between water temperature differences? Help needed
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At atmospheric pressure, how much heat is required to heat 1 kg of water from 20°C to 80°C using steam? There are two ways of calculation: 1. Q = CMT = 4.2 * 1 * (80 – 20); 2. The enthalpy of vaporization of water is 2453 kJ/kg at 20°C and 2308 kJ/kg at 80°C, so Q = (2453 – 2308) * 1. Please help – which method is correct? Or what does the second method mean?
If there is no phase change, heat capacity is used for calculation; if there is a phase change, the enthalpy of vaporization is used. For water ranging from 20°C to 80°C, with a boiling point of 100°C, there is essentially no phase change, so the first method is applied.
The second algorithm isn’t quite appropriate; one can’t use the enthalpy of vaporization for this purpose. Instead, values of enthalpy at different temperatures should be used, and those should be the enthalpy values of water. When water goes from 20 degrees to 80 degrees, there is no phase change.
In principle, both are acceptable. The second error arises from the incorrect use of enthalpy values; the enthalpy of vaporization cannot be used, as that applies to water vapor – the enthalpy value of water is sufficient