Heat and Temperature

Let’s Review - According to the kinetic theory of matter, all matter is made up of tiny particles – called atoms or molecules. - These particles are always moving, and it is this movement that helps decide what state of matter exists (solid, liquid, gas, plasma). - The particles have potential and kinetic energy (kinetic as they are moving, and potential as they are potentially attracted or repulsed by each other). - The TOTAL of all these forms of energy in a particular substance is called its thermal energy

STATES OF MATTER SOLIDS Particles of solids are tightly packed, vibrating about a fixed position. Solids have a definite shape and a definite volume. Heat

STATES OF MATTER LIQUID  Particles of liquids are tightly packed, but are far enough apart to slide over one another.  Liquids have an indefinite shape and a definite volume. Heat

STATES OF MATTER GAS  Particles of gases are very far apart and move freely.  Gases have an indefinite shape and an indefinite volume. Heat

A.Intermolecular Forces 1. the attractive forces between molecules 2. states of matter are determined by the strength of these forces (IMF increase from gas  liquid  solid)

Temperature - When you strike a nail with a hammer, it becomes warm. Why? When you put a flame to a liquid, the liquid becomes warmer as its molecules move faster. Why? - In both the above examples, the molecules are made to race back and forth faster. In other words, they gain kinetic energy. In general, the warmer an object, the more kinetic energy its atoms and molecules possess. - Temperature, the degree of “hotness” or “coldness” of an object, is proportional to the average (NOT total) kinetic energy of the atoms or molecules making it up.

Measuring Temperature Temperature - a quantity that measures the kinetic energy per molecule due to random motion. - The scale most often used world-wide is the Celsius thermometer, where a zero (0) is assigned to the temperature at which water freezes, and 100 is assigned to the temperature at which water boils (at standard atmospheric pressure).

- In the U.S., the number 32 is traditionally assigned to the temperature at which water freezes, and the number 212 is the temperature at which water boils. This thermometer is called the Fahrenheit scale. Measuring Temperature

Upper Limits of Temperature - In principle, there is no upper limit to temperature -As thermal motion increases, a solid object first melts than vaporizes. As the temperature is further increased, molecules dissociate into atoms, and atoms lose some of their electrons, thereby creating a cloud of electrically charged particles – called plasma. - Plasmas exist in stars, where the temperature is many millions of degrees Celsius.

Lower Limits of Temperature - In contrast to high temperatures, there is a definite limit at the opposite end of the scale, called absolute zero. - Temperature is based upon kinetic energy of molecules. The colder something is, the slower the molecules. Eventually, the molecules will slow down SO much, they will essentially stop moving (they will be out of energy, and so they can’t get any colder).

Measuring Temperature

Heat -We know that temperature is the hot or cold nature of something (based on the kinetic energy of its molecules), so what is heat? Heat is the thermal energy transferred from one thing to another due to a temperature difference. - If you touch a hot stove, thermal energy enters your hand because the stove is warmer than your hand. When you touch a piece of ice, thermal energy passes out of your hand and into the colder ice.

-The direction of energy flow is ALWAYS from a warmer thing to a neighboring cooler thing. Transfer of Heat Energy Cup gets cooler while hand gets warmer Ice gets warmer while hand gets cooler

Heat -Heat is the thermal energy transferred from one thing to another due to a temperature difference. -Heat is simply thermal energy in transit. Why do you feel cold on a winter day?

When outdoors on a winter day, you feel chilly not because something called “cold” gets to you, but because you lose body heat (hot to cold) That’s the purpose of your coat – to slow the heat flow from your body to the surrounding air. Cold is just reduced thermal energy. Heat Versus Cold

1 st Law of Thermodynamics -What we’ve learned thus far about heat and thermal energy is summed up in the laws of thermodynamics. The word thermodynamics stems from Greek for “movement of heat.” -When thermal energy transfers as heat, it does so without net loss or gain. The energy lost from one place is gained by the other. This conservation of energy, when specifically applied to thermal systems, is known as the First Law of Thermodynamics: Whenever heat flows into or out of a system, the gain or loss of thermal energy equals the amount of heat transferred. (You can’t get something from nothing because energy and matter are always conserved).

2 nd Law of Thermodynamics -The Second Law of Thermodynamics restates what we’ve learned about the direction of heat flow: Heat never spontaneously flows from a lower-temperature substance to a higher-temperature substance (You can’t break even; you can’t return to the same energy state because entropy always increases). -When heat flow is spontaneous (without the assistance of external work), the direction of the flow is always from hot to cold. Heat can be made to flow the other way only when additional energy is added to the system (like with heat pumps and air conditioners).

Heat Transfer: Conduction - Conduction involves the transfer of heat through direct contact - Heat conductors conduct heat well, insulators do not

Heat Transfer: Convection -Takes place in liquids and gases as molecules move in currents -Heat rises and cold settles to the bottom

Heat Transfer: Radiation -Heat is transferred through space -Energy from the sun being transferred to the Earth