At standard pressure, ammonia melts at 195 K and boils at 240 K. If a sample of ammonia at standard pressure is cooled from 200 K down to absolute zero, what physical constants are needed to calculate the change in
enhtalpy?
I) the heat capacity of ammonia(s)
II) the heat capacity of ammonia(`)
III) the heat capacity of ammonia(g)
IV) the enthalpy of fusion of ammonia
V) the enthalpy of vaporization of ammonia
You need the heat capacity of liquid NH3 to go from 200 K to 195K, the enthalpy of fusion to freeze the liquid NH3 to solid NH3 @ 195, then you need the heat capacity of solid NH3 to go from 195K to zero K.
To calculate the change in enthalpy, we need the following physical constants:
I) The heat capacity of ammonia(s) - required to determine the heat absorbed/released during the cooling process from the initial temperature (200 K) to the freezing point (195 K) of ammonia.
IV) The enthalpy of fusion of ammonia - needed to calculate the heat absorbed/released during the phase change from solid (ammonia(s)) to liquid (ammonia(l)) at its freezing point.
III) The heat capacity of ammonia(g) - needed to determine the heat absorbed/released during the heating process from the freezing point (195 K) to the boiling point (240 K) of ammonia.
V) The enthalpy of vaporization of ammonia - required to calculate the heat absorbed/released during the phase change from liquid (ammonia(l)) to gas (ammonia(g)) at its boiling point.
Note: The heat capacity of ammonia(l) is not explicitly mentioned in the given information but can be approximated using the heat capacity of ammonia(s) and ammonia(g).
To calculate the change in enthalpy of ammonia when it is cooled from 200 K to absolute zero, we need to consider the different phases of ammonia and the energy involved in each phase transition.
The process involves the cooling of ammonia from a gas phase (above its boiling point) to a solid phase (below its melting point). Therefore, the following physical constants are needed to calculate the change in enthalpy:
I) The heat capacity of ammonia(s) - This is required to calculate the energy required to cool ammonia from its gas phase to the solid phase. It represents the amount of heat required to raise the temperature of a given mass of ammonia solid by one unit (usually 1 K or 1°C).
IV) The enthalpy of fusion of ammonia - This is the heat required to convert a certain mass of solid ammonia into an equivalent mass of liquid ammonia at its melting point. It represents the energy needed for the solid-to-liquid phase transition.
V) The enthalpy of vaporization of ammonia - This is the heat required to convert a certain mass of liquid ammonia into an equivalent mass of ammonia vapor at its boiling point. It represents the energy needed for the liquid-to-gas phase transition.
The heat capacity of ammonia(g) is not required in this scenario because the cooling process does not involve the gas phase at any point.