Heating and Cooling Curves Review What happens to

Heating and Cooling Curves

Review What happens to molecules as the temperature increases? Kinetic Energy Increases, they move faster What are on the axis of a phase change diagram? Temperature and Pressure What are three phases that a substance passes through? Solid, liquid, gas Do all phase change diagrams look the same, why? No, different substances change phases under different conditions

Heating Curve � The purpose of a heating curve is to see the temperature change as heat (energy) is added to a system. � From a heating curve you can get a substances melting/freezing point and boiling point

Heating Curve � As heat is added to the solid the temperature increases. � When it reaches the melting point the temperature remains constant until all of the solid has become liquid. Temperature is constant

Heating Curve � Once the substance has all become liquid the temperature will begin to rise again. � The temperature rises until it reaches the boiling point. � Again, the temperature will remain constant until all of the liquid has become vapor/gas

Heating Curve Gas - KE Boiling - PE Liquid - KE Melting - PE Solid - KE

Cooling Curve Cooling curve is the same thing as a heating curve, just in the opposite direction. In this graph we start at high temperatures and get lower. Remember that melting point occurs at the same temperature as freezing point.

Temperature Units In science we typically use two equivalent units of temperature, degrees Celsius and kelvin. The Celsius scale sets the freezing point of water at 00 C and the boiling point at 1000 C. The Kelvin scale sets freezing at 273. 15 kelvin and boiling at 373. 15 kelvin. A change of one degree is equal on each scale. The zero point on the Kelvin scale is considered absolute zero. Since the scales are the same all you have to do to convert from one to the other is add/subtract 273 0 C = K – 273 K = 0 C + 273