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Phase, State and Energy Changes

Phase and State Changes refers to the transformation of a thermodynamic system from one phase or state to another. Although the terms ‘phase’ and ‘state’ are used interchangeably, they are in fact different ways to describe a chemical system. A ‘state’ of matter is a more specific term than a ‘phase’ of matter. The state of matter of a particular system is the state of a particular system within that system, while a phase can not only refer to a set of states within such a system, but also the type of molecular motion as well as pinpointing a particular region in three dimensional space.

A phase or state change usually occurs as a result of a change in an external condition, which changes the energy of the whole system. An increase in temperature would increase the energy of the whole system, giving the matter contained within the defined system more internal/heat energy. If enough energy is applied to the system, solids will change to liquids through the process of melting; liquids will change into gases through the process of vaporization; and gases may even change into plasma through the process of ionization. 

Although phase changes are frequently seen in nature, for example snow melting into water, chemists and engineers may manipulate external conditions in the laboratory to exploit certain types of phase changes. Thus, understanding the thermodynamic rationale behind phase changes is important for understanding the energetics of a given chemical system.

Enthalpy, Entropy, Spontaneous Reactions, & Other Thermodynamics

BCl3(g) + NH3(g) <---> Cl3BNH3(s) (<---> represents equilibrium in this case) The reaction represented above is a reversible reaction. (a) Predict the sign of the entropy change, ΔS, as the reaction proceeds to the right. Explain your prediction. (b) If the reaction spontaneously proceeds to the right, predict the s

Understanding Phase Changes

Problem: Attached is a graph and using this graph, I need to figure out what phase changes are occurring when the temperature is held constant at 150 EC and the pressure is increased from 0.25 atm to 1.4 atm? - Gas-liquid-solid? - Gas-solid-liquid? - Liquid-solid-gas? - Solid-liquid vapor?

Fundamentals of chemistry

The changes in speed and motion of molecules when a solid becomes a liquid and when a liquid becomes a gas. The physical means of separating a heterogeneous mixture of salt and sand. Solving a problem using the scientific method. Please discuss these statements.