Count Rumford supervised the drilling of brass cannons in a factory in Bavaria

16.1 Thermal Energy and Matter

Count Rumford supervised the drilling of brass cannons in a factory in Bavaria.

From his observations, Rumford concluded that heat is not a form of matter.


In what direction does heat flow spontaneously?

Heat is the transfer of thermal energy from one object to another because of a temperature difference.

Work and Heat

Heat flows spontaneously from hot objects to cold objects.


A drill is a machine that does work on the cannon. Remember that no machine is 100% efficient. Some of the work done by the drill is useful, but some energy is lost due to friction.

Heat flows from the cannon to a surrounding water bath because the cannon is at a higher temperature than the water.

Work and Heat


What is the temperature of an object related to?

Temperature

Temperature is related to the average kinetic energy of the particles in an object due to their random motions through space.


Temperature is a measure of how hot or cold an object is compared to a reference point.

• On the Celsius scale, the reference points are the freezing and boiling points of water.

• On the Kelvin scale, absolute zero is defined as a temperature of 0 kelvins.

Temperature


As an object heats up, its particles move faster, on average. The average kinetic energy of the particles increases.

• One way that heat flows is by the transfer of energy in collisions.

• On average, high-energy particles lose energy. Low-energy particles gain energy.

• Overall, collisions transfer thermal energy from hot to cold objects.

Temperature


What two variables is thermal energy related to?

Thermal energy is the total potential and kinetic energy of all the particles in an object.

Thermal Energy

Thermal energy depends on the mass, temperature, and phase (solid, liquid, or gas) of an object.


Thermal energy depends on mass. A cup of tea and a teapot full of tea can have the same temperature.

• The average kinetic energy of the particles is the same in the cup and the pot.

• There is more thermal energy in the teapot because it contains more particles.

Thermal Energy


Thermal energy depends on temperature. Compare a cup of hot tea with a cup of cold tea.

• In both cups, the tea has the same mass and number of particles.

• The average kinetic energy of particles is higher in the hot tea, so it has greater thermal energy.

Thermal Energy


Thermal energy depends on mass and temperature.

A. The tea is at a higher temperature than the lemonade.

B. The lemonade has more thermal energy because it has many more particles.

Thermal Energy


What causes thermal expansion?

Thermal expansion is an increase in the volume of a material due to a temperature increase.

Thermal Contraction and Expansion

Thermal expansion occurs when particles of matter move farther apart as temperature increases.


If you take a balloon outside on a cold winter day, it shrinks in a process of thermal contraction.

• As temperature decreases, the particles that make up the air inside the balloon move more slowly, on average.

• Slower particles collide less often and exert less force.

• Gas pressure decreases and the balloon contracts.

Thermal Energy


If you bring the balloon inside, it expands.

Gases expand more than liquids and liquids usually expand more than solids.

Thermal Energy


As temperature increases, the alcohol in a thermometer expands, and its height increases in proportion to the increase in temperature.

In an oven thermometer, strips of steel and brass expand at different rates as the coil heats up. The coil unwinds, moving the needle on the temperature scale.

Thermal Energy


How is a change in temperature related to specific heat?

Specific heat is the amount of heat needed to raise the temperature of one gram of a material by one degree Celsius.

Specific Heat

The lower a material’s specific heat, the more its temperature rises when a given amount of energy is absorbed by a given mass.


When a car is heated by the sun, the temperature of the metal door increases more than the temperature of the plastic bumper.

The iron in the door has a lower specific heat than the plastic in the bumper.

Specific Heat


Specific Heat


In this formula, heat is in joules, mass is in grams, specific heat is in J/g•°C, and the temperature change is in degrees Celsius.

Specific Heat


Calculating Specific Heat

An iron skillet has a mass of 500.0 grams. The specific heat of iron is 0.449 J/g•°C. How much heat must be absorbed to raise the skillet’s temperature by 95.0°C?

Specific Heat


Read and UnderstandWhat information are you given?

Specific Heat


Read and UnderstandWhat information are you given?

Specific Heat


Plan and Solve

What unknown are you trying to calculate?

What formula contains the given quantities and the unknown?

Specific Heat


Plan and Solve

What unknown are you trying to calculate?

What formula contains the given quantities and the unknown?

Specific Heat


Plan and Solve

Replace each variable with its known value.

Specific Heat


Plan and Solve

Replace each variable with its known value.

Specific Heat


Look Back and CheckIs your answer reasonable?

Specific Heat


Look Back and CheckIs your answer reasonable?

Round off the data to give a quick estimate.

Q = 500 g × 0.5 J/g•°C × 100°C = 25 kJ

This is close to 21.4 kJ, so the answer is reasonable.

Specific Heat


1. How much heat is needed to raise the temperature of 100.0 g of water by 85.0°C?

Answer:

Specific Heat


1. How much heat is needed to raise the temperature of 100.0 g of water by 85.0°C?

Answer:

Q = m * c * ∆T = (100.0 g)(4.18 J/g•°C)(85.0°C)

= 35.5 kJ

Specific Heat


2. How much heat is absorbed by a 750-g iron skillet when its temperature rises from 25°C to 125°C?

Answer:

Specific Heat


2. How much heat is absorbed by a 750-g iron skillet when its temperature rises from 25°C to 125°C?

Answer:

Q = m * c * ∆T = (750 g)(0.449 J/g•°C)(125°C – 25°C)

= (750 g)(0.449 J/g•°C)(100°C)

= 34 kJ

Specific Heat


3. In setting up an aquarium, the heater transfers 1200 kJ of heat to 75,000 g of water. What is the increase in the water’s temperature? (Hint: Rearrange the specific heat formula to solve for ∆T.)

Answer:

Specific Heat


3. In setting up an aquarium, the heater transfers 1200 kJ of heat to 75,000 g of water. What is the increase in the water’s temperature? (Hint: Rearrange the specific heat formula to solve for ∆T.)

Answer: ∆T = Q / (m x c)= 1,200,000 J/(75,000 g × 4.18 J/g•°C)

= 3.8°C

Specific Heat


4. To release a diamond from its setting, a jeweler heats a 10.0-g silver ring by adding 23.5 J of heat. How much does the temperature of the silver increase?

Answer:

Specific Heat


4. To release a diamond from its setting, a jeweler heats a 10.0-g silver ring by adding 23.5 J of heat. How much does the temperature of the silver increase?

Answer: ∆T = Q / (m x c)= 23.5 J/(10.0 g × 0.235 J/g•°C)

= 10.0°C

Specific Heat


5. What mass of water will change its temperature by 3.0°C when 525 J of heat is added to it?

Answer:

Specific Heat


5. What mass of water will change its temperature by 3.0°C when 525 J of heat is added to it?

Answer: m = Q / (∆T x c)= 525 J/(3.0°C × 4.18 J/g•°C)

= 42 g

Specific Heat


On what principle does a calorimeter operate?

A calorimeter is an instrument used to measure changes in thermal energy.

Specific Heat

The lower a material’s specific heat, the more its temperature rises when a given amount of energy is absorbed by a given mass.


According to the law of conservation of energy, the thermal energy released by a test sample is equal to the thermal energy absorbed by its surroundings.

The calorimeter is sealed to prevent thermal energy from escaping.

Specific Heat


A calorimeter is used to measure specific heat. A sample is heated and placed in the calorimeter. The temperature change is observed.

Specific Heat


Assessment Questions

1. What is the thermal energy of an object? a. the total number of atoms or molecules

b. the total kinetic energy of the atoms or molecules

c. the average kinetic energy of the atoms or molecules

d. the average mechanical energy of the atoms or molecules



1. What is the thermal energy of an object? a. the total number of atoms or molecules

b. the total kinetic energy of the atoms or molecules

c. the average kinetic energy of the atoms or molecules

d. the average mechanical energy of the atoms or molecules

ANS: B



2. What causes a gas to expand when its temperature is increased?a. The number of particles increases as temperature

increases.b. Each particle expands as its temperature increases, so

the total volume increases.c. As temperature increases, more electrons leave atoms

and move separately.d. As gas particles move faster, they overcome some

forces of attraction.



2. What causes a gas to expand when its temperature is increased?a. The number of particles increases as temperature

increases.b. Each particle expands as its temperature increases, so

the total volume increases.c. As temperature increases, more electrons leave atoms

and move separately.d. As gas particles move faster, they overcome some

forces of attraction.

ANS: D



3. The specific heat of water is 4.18 J/g•°C. How much heat is required to raise the temperature of 1,000 grams of water by 50°C? a. 83.6 J

b. 83.6 kJ

c. 209 J

d. 209 kJ



3. The specific heat of water is 4.18 J/g•°C. How much heat is required to raise the temperature of 1,000 grams of water by 50°C? a. 83.6 J

b. 83.6 kJ

c. 209 J

d. 209 kJ

ANS: D



4. What property of matter can be measured using a calorimeter? a. temperature

b. thermal expansion

c. specific heat

d. mass



4. What property of matter can be measured using a calorimeter? a. temperature

b. thermal expansion

c. specific heat

d. mass

ANS: C



1. Temperature is the transfer of thermal energy from one object to another.

TrueFalse



1. Temperature is the transfer of thermal energy from one object to another.

TrueFalse

ANS: F, Heat

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Count Rumford supervised the drilling of brass cannons in a factory in Bavaria