1. HEAT TRANSFER AND CHANGE OF STATE By: Krissia Mae Doniza

2. HEAT TRANSFER  Heat Transfer, in physics, process by which energy in the form of heat is exchanged between bodies or parts of the same body at different temperatures. Heat is generally transferred by convection, radiation, or conduction.

3. Conduction  Occurs when two object touch  If the temperature at one end of a metal rod is raised by heating, heat is conducted to the colder end.

4.  Materials such as gold, silver, and copper have high thermal conductivities and conduct heat readily, this are called conductors  materials such as glass and asbestos have values of thermal conductivity hundreds and thousands of times smaller, conduct heat poorly, are called insulator. Conduction

5. Convection  Occurs when the heated substances moves itself.  If a liquid or gas is heated, its mass per unit volume generally decreases. If the liquid or gas is in a gravitational field, the hotter, lighter fluid rises while the colder, heavier fluid sinks. This kind of motion, due solely to no uniformity of fluid temperature in the presence of a gravitational field is an example of nature convection.

6. Radiation  Occur in empty space, such as in outer space  Any energy transferred by this method is radiant energy

7.  When the atoms and molecules are no longer closely associated with one another, all bonds have been broken and the liquid has become a gas. In gaseous state, each atom or molecule is no longer surrounded by several neighbors but occasionally bumps into another atoms or molecule. CHANGE OF STATE

8.  Previous heat equation: Q = mcΔT Covers the temperature changes, but we also need to be able to compute the heat needed to change from one state to another. CHANGE OF STATE

9. Q f =m H f In melting, it takes amount of heat to change from solid to a liquid Q f = amount of heat in kcal, m = mass of solid in kg, H f = the heat of fusion in kcal/, for water H f is 80 kcal/kg Melting and Heat of Fusion

10. Q v =mH v In evaporating, it takes an amount of heat To change from a liquid to a gas Q v =amount of liquid in kg H v =the heat of vaporazation in kcal/kg.for water is 540 kcal/kg Evaporation and Heat of Vaporization

11.  The change of solid into gas  The reason that solid carbon dioxide, CO 2, is used to keep ice cream frozen while being shipped.  Ex. Dry ice solid CO 2 change directly to gas. Sublimation

12. The amount of heat Q total needed to turn a mass, m of ice at some initial temperature T i into gas at a final temperature T f can be computed by the following equation: Q total = mc ice (T m -T i ) + mH f + mc wate r (T v -T m ) + mH v + mc wv (T f -T v ) T m = melting temperature of ice(o°C) c ice, c water and c wv =are especifec heats of ice, water and water vapor, in kcal/kg°C T v =boiling temperature of water,100°C Equation for Change of State

13. Or Q total = mc ice (T m -T i ) + mH f + mc wate r (T v -T m ) + mH v + mc steam (T f -T v )  This equation is used to determine the amount of heat needed to convert a material from one state to another.  Increasing temperature Q total is beat gained  Decreasing temperature Q total of heat lost Equation for Change of State