intermolecular forces

Is known as the critical temperature tc and the

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is known as the critical temperature (Tc) and the pressure at which this occurs is known as the critical pressure (Pc) supercritical fluids have properties of both liquids and gases, while being neither, and sometimes an intermediate of both Sublimation a transition directly from a solid to a gas state is known as sublimation the opposite of this transition, deposition , occurs when gas molecules become deposited within a solid and are stuck by intermolecular forces Fusion at a certain temperature, the melting point (0˙C for water), molecules have enough thermal energy to change state from a solid into a liquid the process of melting is also known as fusion , the transition from solid to liquid the opposite of this melting or fusion is freeing , the transition from liquid to solid once the melting point of a solid is reached, additional heating will only increase the rate of melting it will not increase the temperature of the liquid water past 0˙C. only once all the solid has melted will the liquid water be able to experience an increase in temperature a mixture of ice and water will always have a temperature of 0˙C at 1 atm Energetics of Melting and Freezing the most common way of cooling a beverage is to drop ice cubes in it because melting is an endothermic process and requires heat from the liquid the amount of heat required to melt 1 mol of a solid is called the heat of fusion ∆H_fus, which is 6.02 kJ/mol for water the heat of fusion is always positive because melting is endothermic (it requires energy to melt things and break bonds) freezing, the opposite of melting, is exothermic and releases energy into the environment
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as liquid becomes a solid (bonds form) and this has the same magnitude but opposite sign of fusion in general the heat of fusion is a lot less than the heat of vaporization because to change a solid into a liquid, which are much closer in properties than solids and gases, the intermolecular forces only need to be partially overcome whereas with liquid to gas in vaporization, the intermolecular forces must be completely overcome. Melting means that molecules can move around one another while still remaining in contact the heating curve for water summarizes the steps of transition from ice to steam:
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the temperature is constant in stages 2 and 4 as the extra heat added is required to speed up the process of changing state and, therefore, is not involved with increasing the temperature until the state change is complete during the transition between states, the two states are in equilibrium and the temperature remains constant, the amount of heat required for state change is given by: during stages 1, 3, and 5 the temperature rises linearly within a single state in accordance with the substance's heat capacity:
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