Chapter 21: Temperature, Heat and Expansion

What is “normal” body temperature and what instrument is used to measure it? 98.6 degrees Fahrenheit A thermometer

What are the three temperature scales? Fahrenheit Celsius Kelvin

Fahrenheit Scale Water boils at 212 degrees and freezes at 32 degrees There are 180 degrees between the freezing point and boiling point of water.

Celsius Temperature Scale Water freezes at 0 degrees and boils at 100 degrees There are 100 degrees between the freezing point and boiling point of water. Some people refer to this as the Centigrade scale (cent=100).

Kelvin Scale SI scale of temperature/used in scientific research Degrees are same “size” as the Celsius degree and are called kelvins 0 is the lowest possible temperature, called absolute zero (no kinetic energy) corresponds to -273 degrees Celsius Water freezes at 273 K and boils at 373 K

Temperature and Kinetic Energy Temperature is the measure of the average kinetic energy of the molecules in a material. Why do you think it’s the average kinetic energy and not the total kinetic energy?

Heat Heat and temperature are not the same thing!! Heat is the energy that flows from one object to another due to a difference in temperature.

Thermal Contact Thermal = heat Contact = two objects or substances that are touching Objects are in thermal contact when heat energy flows from objects or substances that are touching.

Thermal Equilibrium Occurs when two objects that are touching reach the same temperature.

Does leaving the refrigerator door open let the cold air out or the warm air in? Warm air in (heat flows from high to low temperature) Heat never flows on its own from a cooler substance to a hotter substance!

Internal Energy Internal energy is the grand total of all energies inside a material. potential energy, kinetic energies An object does not contain heat, it contains internal energy.

Measurement of Heat Energy Heat energy is measured in calories or Calories (1,000s of calories) 1 Calories = 1 kilocalorie (1,000 calories) The calorie and Calorie are units of energy. 1 calorie = J

Definition of calorie and Calorie A calorie is the amount of heat required to raise the temperature of 1 gram of water by 1-degree Celsius. A Calorie (kilocalorie) is the amount of heat needed to raise the temperature of 1 kilogram of water by 1-degree Celsius.

Food is burned to determine the calories

Determining calories (energy) in food The energy value in food is determined by burning the food and measuring the energy that is released as heat. Food and other fuels are rated by how much energy a certain mass of the fuel gives off as heat when burned.

Question Why is sand on a beach very hot on a hot summer day, but very cool at night? Why does the sand temperature change so much between day and night, but the ocean water temperature stay about the same?

Specific Heat Capacity The quantity of heat needed to raise the temperature of a unit of mass of a substance one degree Celsius. Things that take a long time to heat up and cool down have a high specific heat capacity. Things that heat up and cool down fast have a low specific heat capacity.

Specific Heat Capacity Also refers to a material’s capacity to store internal energy. Materials that need a lot of energy to raise its temperature have a high specific heat capacity.

Specific Heat Capacity Which has the lower specific heat capacity on a pizza, the dough for the crust or the tomato sauce?

High Specific Heat Capacity of Water Water has a much higher capacity for storing energy than most common materials. What are some benefits of water’s high specific heat capacity?

Some benefits of the high specific heat capacity of water Cooking Bathing Heating and Cooling Systems (car radiators) Climate (San Francisco vs. Washington DC)

Thermal Expansion Expansion joints Bimetallic Strip –thermostats

Expansion of Water Water is densest at 4-degrees Celsius –Begins to expand at 3 and 5-degrees Celsius

Benefit of 4-degree Celsius Water Temperature