A few small questions; feel free to discuss them – there are prizes for the best discussions
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This post was last edited by kaminocmyhc on 2010-9-10 at 14:22. My calculation gives a value of 49.61 kj/mol. Please verify this. If a substance needs to be heated to 115 degrees Celsius, the heat carrier that can be used is: The answer is B, atmospheric pressure steam; I think this is clearly incorrect – it should be C, pressurized steam, or D, molten salt mixture. The most commonly used cooling water in chemical plants is: the answer is B, deep well water. I think it’s incorrect; it should be C circulating water (secondary water). Please have an expert confirm this
This post was last edited by kaminocmyhc on 2010-9-10 at 14:24. Steam with a pressure of less than 1.6 MPa is at normal pressure; heating it to 115 degrees Celsius is sufficient. The most commonly used cooling water in chemical plants is usually treated circulating water
For heating, steam at normal pressure is generally sufficient; we use steam with a pressure of 0.35 Mpa for heating.
Is 18g equal to 1 mol, or is 1g equal to 18 mol?
------------------------------- 1 mol H2O is 18 g; -------------------------------
2756/1000=2.756/18=0.1531 (Kj/mol). This clearly can’t be right; 1 mole of water vapor weighs 18 grams, right?
The original poster is right; the answer given by the second poster is wrong. The molar density of water vapor is 18 g/mol. The specific enthalpy of water vapor is 2756 KJ/kg. The molar enthalpy of water vapor equals the specific enthalpy multiplied by the molar density: 2756 KJ/kg * 18 g/mol = 2.756 KJ/g * 18 g/mol = 49.608 KJ/mol.
Generally, when heating above 100 degrees Celsius, pressurized steam is preferred as it is easy to use, provides stable temperatures, and is also less costly. After all, salt-soluble mixtures are used very rarely, and they are inconvenient to handle; the equipment required for using them is also difficult to work with.
The average annual temperature of water from ordinary wells ranges between 8 degrees Celsius and 15 degrees Celsius. If the water is readily available in large quantities, it can also be a good option; however, an unlimited supply cannot be ensured. The temperature of circulating water is generally above 20 degrees Celsius, and the cooling system for such water also consumes a lot of energy; however, it is able to ensure a stable supply.
For a substance, the mass of 1 mole is its molecular weight, which is independent of its state; therefore, 1 mole of water or water vapor both weighs 18 g.
Low-pressure steam can be heated to 115 degrees Celsius; this is not possible with atmospheric pressure. The most commonly used cooling water in chemical plants is treated circulating water