Explanation:
represents the phase transitions that a substance undergoes as heat is added to it.
The plateaus on the curve mark the phase changes. The temperature remains constant during these phase transitions.
Water has a high boiling point because of the strong hydrogen bonds between the water molecules; it is both a strong hydrogen bond donor and acceptor.
The first change of phase is melting, during which the temperature stays the same while water melts. The second change of phase is boiling, as the temperature stays the same during the transition to gas.
Terms
hydrogen bondA strong intermolecular bond in which a hydrogen atom in one molecule is attracted to a highly electronegative atom (usually nitrogen or oxygen) in a different molecule.
specific heat capacityThe amount of heat needed to raise the temperature of 1 g of a substance by 1 degree Celsius.
Like many substances, water can exist in different phases of matter: liquid, solid, and gas. A heating curve shows how the temperature changes as a substance is heated up at a constant rate.
Drawing a Heating Curve
Temperature is plotted on the y-axis, while the x-axis represents the heat that has been added. A constant rate of heating is assumed, so that one can also think of the x-axis as the amount of time that goes by as a substance is heated. There are two main observations on the measured curve:
regions where the temperature increases as heat is added
plateaus where the temperature stays constant.
It is at those plateaus that a phase change occurs.
Heating Curve of WaterThe phase transitions of water.
Analysis of a Heating Curve
Looking from left to right on the graph, there are five distinct parts to the heating curve:
Solid ice is heated and the temperature increases until the normal freezing/melting point of zero degrees Celsius is reached. The amount of heat added, q, can be computed by:
