Question

Part A

For each phase change, determine the sign of and .

Sublimation , Freezing,Condensation, Deposition, Boiling , Melting

a)   +ΔH,+ΔS

b) -ΔH, -ΔS

c) +ΔH, -ΔS

d) -ΔH, +ΔS

Put the phase change to the correctsign of ΔH and ΔS

Answer 1

Concepts and reason

The change in energy $\left( {\Delta H} \right)$ during phase change or during a reaction is known as Enthalpy. When energy is absorbed during reaction or phase change the sign for enthalpy is taken as positive and when energy is released during reaction or phase change the sign for enthalpy is taken as negative.

The change in entropy (degree of randomness, $\Delta S$ ) during phase change or during a reaction is known as Entropy. When the degree of randomness is increased, it is given a positive sign and when degree of randomness is decreased, it is given a negative sign.

In the given question, you need to determine the signs of $\Delta H$ and $\Delta S$ for various process mentioned in the question.

Fundamentals

Sublimation – The process in which a substance in solid state is directly converted into gaseous state is termed as sublimation.

Freezing - The process in which a substance in liquid state is converted into solid state is termed as freezing.

Condensation - The process in which a substance in gaseous state is converted into liquid state is termed as condensation.

Deposition - The process in which a substance in gaseous state is directly converted into solid state is termed as deposition.

Boiling - The process in which a substance in liquid state is converted into gaseous state is termed as boiling.

Melting - The process in which a substance in solid state is converted into liquid state is termed as melting.

For sublimation, the change in energy is positive and the change in randomness is also positive.

For freezing, the change in energy is negative and the change in randomness is also negative.

For condensation, the change in energy is negative and the change in randomness is also negative.

For deposition, the change in energy is negative and the change in randomness is also negative.

For boiling, the change in energy is positive and the change in randomness is also positive.

For melting, the change in energy is positive and the change in randomness is also positive.

Ans:

The sign of $\Delta H$ and $\Delta S$ for sublimation process is