Get Heating Curve And Heat Transfer - Aug

The lines are curved because as the substance cools, the temperature difference between the surroundings and the substance is reduced. This reduces the rate at which heat is transferred out of the substance, reducing the rate of cooling.

A phase change along the heating curve is perceived as endothermic while a phase change along the cooling curve is seen as exothermic. For instance, if the phase change is from the state of solid to liquid, then the phase change is endothermic since the transition of state of matter is from orderly to less orderly.

1: A typical heating curve for a substance depicts changes in temperature that result as the substance absorbs increasing amounts of heat. Plateaus in the curve (regions of constant temperature) are exhibited when the substance undergoes phase transitions. Consider the example of heating a pot of water to boiling.

Cooling curves show the exothermic processes, which is the opposite of the endothermic processes the heating curve shows. The cooling curve is the exact same as the heating curve, but it has the heats of condensation and heats of freezing instead.

Heating curves show how the temperature changes as a substance is heated up. Cooling curves are the opposite. They show how the temperature changes as a substance is cooled down. Just like heating curves, cooling curves have horizontal flat parts where the state changes from gas to liquid, or from liquid to solid.

The aim of heating curve of water is to show how the temperature of a known amount of water changes as constant heat is added. In contrast, the cooling curve of water is to show the temperature of a known amount of water changes as constant heat is released.

Heat of fusion, ΔHfus, is the heat energy necessary to convert a given amount of solid to liquid at constant pressure. (In this context, fusion is another word for melting.) The units for ΔHfus vary, but it is commonly described in J/g. Like specific heat capacities, heats of fusion vary from one substance to another.

For example, this is the heating curve for iron, a metal that melts at 1538°C and boils at 2861°C. Heating curves show how the temperature changes as a substance is heated up. Cooling curves are the opposite. They show how the temperature changes as a substance is cooled down.