Temperature, Heat, and Expansion

Temperature, Heat, and Expansion

absolute zerobimetallic stripcalorieCelsius scaleFahrenheit scaleheatinternal energyKelvin scalekilocaloriespecific heat capacitytemperaturethermal contactthermal equilibriumthermostat Key words to define: (light blue physics book)

--The kinetic theory of matter states that all matter is made up of tiny particles (molecules) in constant motion.--We sense kinetic energy as heat.--As the molecules in an object move faster, the object becomes warmer.--If you cool off an object, its particles move slower.

Temperature--Temperature is how hot or cold something is compared to a standard.--Almost all matter expands when temperature increases and contracts when temperature decreases. A thermometer measures temperature by contraction and expansion of a liquid.

--Celsius is the most widely used scale, based on the freezing and boiling points of water. This scale is divided into 100 degrees.--Fahrenheit is still used in the US, with water freezing at 32° and boiling at 212°.--Kelvin is the scale used in scientific research, where zero is the lowest possible temperature (absolute zero).

Temperature and Kinetic Energy--Temperature is proportional to the average translational kinetic energy of molecular motion of the particles in a material. Potential energy is also involved with solids and liquids.--Temperature is an average not total. KE ≠ temperature, its proportional

Heat--The direction of spontaneous heat transfer is always from warmer to cooler substances.--Objects do not contain heat, they contain thermal energy. Heat is the flow of that energy. This energy is called internal energy.

--When two objects are in thermal contact, heat moves from the higher temperature to the lower temperature object.--A large object may have more thermal energy but a lower temperature than another object. What happens when the two objects come into thermal contact?

Thermal Equilibrium--Equilibrium occurs when two objects in thermal contact reach the same temperature. Same temperature = no energy movement.--That is why thermometers require a waiting period. They have to reach thermal equilibrium.

Internal Energy--Objects have translational kinetic energy, rotational kinetic energy, kinetic energy of atoms in molecules, and potential energy between molecules. These are collectively called internal energy.--Ice melts as it gains heat, but…?

Measurement of Heat--When we measure heat (not temp.), we need to know the mass and the type of material affected. We compare this value to the change in temperature of water, because it is so common.

--The unit for heat is the calorie. 1 calorie is the heat required to raise the temperature of 1g of water by 1°C--A kilocalorie is 1000 calories. A kilocalorie is how we measure food energy. We use the capital Calorie to refer to food calories.--The metric unit for heat is Joules, with 1 cal = 4.18 J

How many joules are in a 20oz. Dr. Pepper?(According to the label, a Dr. Pepper bottle has 100 Cal per serving and contains 2.5 servings)

Specific Heat Capacity--Different substances have different capacities for storing internal energy.--Absorbed energy can affect substances in different ways: could increase the translational speed of molecules, the rotational speed of molecules, or stretch the forces between molecules.

--compare a steel pan and aluminum foil after being removed from a hot oven--compare sand and water at the beach on a hot summer day--compare the crust of a freshly microwaved Hot Pocket from its filling--The amount of energy needed to raise the temperature of a material is called the Specific heat capacity, or just specific heat.

Q = mcΔTQ = the amount of heatm = the mass in gramsc = the specific heat of the materialΔT = the change in temperature in °C or K

How much heat would be lost from a 220g steel pan after removing it from a 175°C oven and allowing it to cool to 45°C?(cFe = .450 J/g·K)How much heat would water lose with the same mass under the same conditions?(cH2O = 4.18 J/g·K)

The High Specific Heat Capacity of Water--Water can resist changes in its temperature. It is used as a cooling agent for other objects, as well as a warming agent for cool objects. --Because of this, water is a climate changer. Europe would be frozen like Canada, if not for the air and water currents bringing warm air to it.

Thermal Expansion--Because faster moving particles spread out, objects tend to expand as their temperatures increase. --Liquids expand or contract more than solids, while gases expand or contract much more than liquids.--ex. sidewalk cracks, creaking houses

--Bimetallic strips are used to turn pointers, regulate valves, or operate switches.--A thermostat is a bimetallic strip that turns A/C-Heating systems on and off.--Thermal expansion causes glass to break, gas to overflow the gas tank, and thermometers to work.

Expansion of Water--Water is an exception to the contraction while cooling rule. The most dense water can be is at 4°C. Cooler than that, and the water molecules begin to expand. Once it is ice, cooler temperatures cause it to contract just like everything else.--This is caused by water’s bent shape and its ability to hydrogen bond.

--Because of this exception, ice does something that no other solid does in its liquid…if floats. All other solids sink in their liquids, because the solid phase is more dense. This allows fish in lakes and ponds to survive the winter. Ice floats up to the top, providing an insulating layer from extremely cold temperatures.

Temperature, Heat, and Expansion