SpecificSpecific HeatHeat

The specific heat of a The specific heat of a substance is the quantity substance is the quantity of heat required to of heat required to change the temperature change the temperature of 1 g of that substance of 1 g of that substance by 1by 1ooC.C.

The units of The units of specific heat in specific heat in joules arejoules are:: o

Joulesgram Celcius

oJ

g C

The units of The units of specific heat in specific heat in calories arecalories are:: o

caloriesgram Celcius

oJ

g C

The relation of mass, specific heat, The relation of mass, specific heat, temperature change (temperature change (ΔΔtt), and quantity of ), and quantity of heat lost or gained is expressed by the heat lost or gained is expressed by the general equation:general equation:

Δt = heatmass of substance)(specific heat

of substance)(

Example 1Example 1

o1638 J

125 g x 27.6 C

Calculate the specific heat of a solid in Calculate the specific heat of a solid in J/gJ/gooC and in cal/ gC and in cal/ gooC if 1638 J raise the C if 1638 J raise the temperature of 125 g of the solid from temperature of 125 g of the solid from 25.025.0ooC to 52.6C to 52.6ooC.C.(mass of substance)(specific heat of substance)Δt = heat

(g)(specific heat of substance)Δt = heatheatspecific heat =

g x Δt

heat = 1638 Jmass = 125 g

Δt = 52.6oC – 25.0oC = 27.6oC

specific heat = o0.475 J=

g C

Calculate the specific heat of a solid in Calculate the specific heat of a solid in J/gJ/gooC and in cal/ gC and in cal/ gooC if 1638 J raise the C if 1638 J raise the temperature of 125 g of the solid from temperature of 125 g of the solid from 25.025.0ooC to 52.6C to 52.6ooC.C.

o0.114 cal=

g Co0.475 J

g C

1.000 cal4.184 J

specific heat =

Convert joules to calories using 1.000 cal/4.184 J

Example 2Example 2

A sample of a metal with a mass of A sample of a metal with a mass of 212 g is heated to 125.0212 g is heated to 125.0ooC and then C and then dropped into 375 g of water at dropped into 375 g of water at 240.0240.0ooC. If the final temperature of C. If the final temperature of the water is 34.2the water is 34.2ooC, what is the C, what is the specific heat of the metal?specific heat of the metal? When the metal enters the water, it begins to cool, losing heat to the water. At the same time, the temperature of the water rises. This process continues until the temperature of the metal and the temperature of the water are equal, at which point (34.2oC) no net flow of heat occurs.

A sample of a metal with a mass of A sample of a metal with a mass of 212 g is heated to 125.0212 g is heated to 125.0ooC and then C and then dropped into 375 g of water at dropped into 375 g of water at 240.0240.0ooC. If the final temperature of C. If the final temperature of the water is 34.2the water is 34.2ooC, what is the C, what is the specific heat of the metal?specific heat of the metal?

Calculate the heat gained by the water.Calculate the heat gained by the water.

Calculate the final temperature of the metal.Calculate the final temperature of the metal.

Calculate the specific heat of the metal.Calculate the specific heat of the metal.

A sample of a metal with a mass of A sample of a metal with a mass of 212 g is heated to 125.0212 g is heated to 125.0ooC and then C and then dropped into 375 g of water at dropped into 375 g of water at 240.0240.0ooC. If the final temperature of C. If the final temperature of the water is 34.2the water is 34.2ooC, what is the C, what is the specific heat of the metal?specific heat of the metal?

Δt = 34.2oC – 24.0oC = 10.2oCtemperature rise of the water

Heat Gained by the Water

o(10.2 C) = (375 )g o4.184 J

g C

heat gained by the water = 41.60 x 10 Jheat lost by the metal

A sample of a metal with a mass of A sample of a metal with a mass of 212 g is heated to 125.0212 g is heated to 125.0ooC and then C and then dropped into 375 g of water at dropped into 375 g of water at 240.0240.0ooC. If the final temperature of C. If the final temperature of the water is 34.2the water is 34.2ooC, what is the C, what is the specific heat of the metal?specific heat of the metal?

Δt = 125.0oC – 34.2oC = 90.8oCtemperature drop of the metal

Once the metal is dropped into the water, its temperature will drop until it reaches the same temperature as the water (34.2oC).

A sample of a metal with a mass of 212 g is A sample of a metal with a mass of 212 g is heated to 125.0heated to 125.0ooC and then dropped into C and then dropped into 375 g of water at 240.0375 g of water at 240.0ooC. If the final C. If the final temperature of the water is 34.2temperature of the water is 34.2ooC, what is C, what is the specific heat of the metal?the specific heat of the metal?

heatspecific heat = mass x Δt

4

o1.60 x 10 J

(212g)(90.8 C)

o0.831 J

g C)

specific heatof the metal =

The heat lost or gained by the system is given by:

(mass) (specific heat) (Δt) = energy change

rearrange

Energy in Energy in Chemical ChangesChemical Changes

In all chemical In all chemical changes, matter changes, matter either absorbs or either absorbs or releases energyreleases energy..

Energy Release From Chemical Sources

Type of Energy Energy Source

Electrical Storage batteries

Light A lightstick. Fuel combustion.

Heat and Light Combustion of fuels.

Body Chemical changes occurring within body cells.

Chemical Changes Caused byAbsorption of Energy

Type of Energy Chemical Change

Electrical Electroplating of metals. Decomposition of water into hydrogen and oxygen

Light Photosynthesis in green plants.

Conservation of Conservation of EnergyEnergy

An energy transformation occursAn energy transformation occurswhenever a chemical change whenever a chemical change occurs.occurs.

If energy is absorbed during a chemical If energy is absorbed during a chemical change, the products will have more change, the products will have more chemical potential energy than the chemical potential energy than the reactants.reactants.

• If energy is given off in a chemical change, the products will have less chemical potential energy than the reactants.

4.4

H2 + O2 have higher potential energy than H2O

energy is given offenergy is absorbed

Electrolysis of Water Burning of Hydrogen in Air

higher potential energy lower potential energy

Law of Law of Conservation of Conservation of EnergyEnergy

Energy can be neither created nor destroyed, Energy can be neither created nor destroyed, though it can be transformed from one form of though it can be transformed from one form of energy to another form of energy.energy to another form of energy.