Heat and Temperature Heat and Temperature Is it

• Heat and Temperature

Heat and Temperature • • • Is it cold in here? How about outside? What would people in Florida think? – The words “hot” and “cold” are not very exact. They depend on a person’s opinion. – Temperature readings help us to “standardize” whether something is “hot” or “cold” – But what does temperature really indicate?

What happens when matter and energy interact? – · Everything in the universe is made up of matter. Matter is anything that has mass and volume (space). Atoms are the smallest particles of matter. Molecules are created when atoms combine with each other. So, atoms and molecules make up everything in the universe. •

• · All matter is made of particles that are … constantly moving. Each particle therefore has kinetic energy. The average KE of all the particles in an object tells us the temperature of the object. – If the particles in a substance are moving faster, the substance has a higher temperature. If the particles in a substance are moving slower, the substance has a lower temperature.

What is Temperature? • Temperature is a measure of the average kinetic energy of the particles in a substance. – What is the difference between a glass of hot water and a glass of cold water? The particles in a glass of hot water are moving faster than those in cold water, therefore the glass of hot water has a greater kinetic energy and temperature. – · What has a higher temperature, an iceberg or cup of hot water? – A cup of hot water has a higher temperature because it has a higher KE per molecule. – · What has more total energy (PE + KE), an iceberg or a cup of hot water? – An iceberg has more total energy. It has many, many more molecules than a cup of hot water.

What is Thermal Expansion? – Thermal expansion refers to the fact that when most matter is heated (solids, liquids and gases), the space between the particles (atoms and molecules) increases the particles expand. When matter loses heat, the particles contract (space between the particles decreases). v The expansion joints on bridges allow the bridge to expand during hot weather and contract in v cold weather (without breaking down the v bridge. )

How does a liquid thermometer work? – · Thermometers are used to measure temperature (or average KE of particles) of matter. – · Liquid thermometers are based on the principle of thermal expansion. When the alcohol in thermometer absorbs heat, the alcohol expands and rises. When it loses heat the alcohol contracts and sinks. This causes the temperature to go up and down. – · The liquid in thermometer comes to thermal equilibrium (equal balance) with the object being measured.

Temperature Scales • Daniel Gabriel Fahrenheit (1686 -1736) developed the first mercury thermometer in 1714. His scale used the temperature of a brine solution of ice and salt as 0°. He chose 30° for the freezing temperature of water and 90° for the temperature of the human body. These were later adjusted to 32° and 98. 6°. •

• Anders Celsius (1701 -1744) developed the centigrade (Celsius) temperature scale assigning 0° to the freezing point of pure water and 100° to the boiling point of pure water. •

• William Thomson (1824 -1907) later Lord Kelvin, developed the absolute temperature scale in 1848. Kelvin realized that gas decreased by 1/273 of its volume for each Celsius-degree decrease in temperature. • Kelvin theorized that a substance would lose all energy at a temperature of -273°C, so he assigned that point a value of 0 on his scale. •

Practice: A. A bowl of soup is 82°C. Convert to °F. 1 and 2. 3. B. A black hole is 3 K. Convert to °C. 4. 1 and 2. 3. C. The sun’s core is 27, 000 °F. Convert to K. 4. 1 and 2. 3. How to convert from one scale to another: 1 Choose appropriate conversion formula 2 Write the formula (as shown above) 3 Substitute temperature into the formula 4 Calculate. Label scale.

What is Heat Energy? • Heat Energy is the energy that is transferred between objects that are of different temperatures. • If heat is transferred energy, then what form of • energy is being transferred? – Thermal energy is the energy being transferred; it is the total kinetic energy of the particles that make up a substance. This energy is measured in joules (J).

The total amount of thermal energy of a substance depends on two factors: 1. Temperature: the higher the temperature, the more thermal energy it has. 2. Amount of a substance: the more particles there are in a substance at a given temperature, the greater thermal energy of the substance (remember, KE depends on mass and speed). •

• Which has a higher temperature: a cup of boiling soup or a bowl of boiling soup? They are the same. This is because the average kinetic energy of the particles in the cup and bowl is moving at same speed. • Which has more thermal energy: a cup of boiling soup or a bowl of boiling soup? The bowl. This is because there are many more particles in the bowl of soup (and each particle has some thermal energy)

In which direction does Heat Flow? • Heat is energy that always flows from matter with a higher temperature to matter with a lower temperature. • • For Example: • What happens when you make a snow ball with your bare hands? • Your hot hands feel cold. • Heat flows from hot hands to the cold snowball. • Your hand transferred heat energy.

• What happens when you place a hot dish from the oven on the counter? • Heat flows from hot dish to cooler counter. • The counter absorbed heat energy and the dish released heat energy.

What is Thermal Equilibrium? • Heat energy moves between objects of different temperatures. Thermal equilibrium occurs when heat energy is transferred between objects of different temperatures until the temperature of all objects are equal (the same). For example: – · A pint of ice cream is placed on the counter. The heat energy from the warmer surroundings (counter and air) will transfer to the ice cream until all three substances are at the same temperature. – · Ice is placed in a glass of warm soda. The heat will transfer from the warm soda to the cold ice until both the soda and ice are the same temperature.