Specific Heat

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

The units of specific heat in joules are:

The units of specific heat in calories are:

The relation of mass, specific heat, temperature change ( Δ t), and quantity of heat lost or gained is expressed by the general equation: ΔtΔt=heat mass of substance )( specific heat of substance )(

Example 1

Calculate the specific heat of a solid in J/g o C and in cal/ g o C if 1638 J raise the temperature of 125 g of the solid from 25.0 o C to 52.6 o C. (mass of substance)(specific heat of substance)Δt = heat (g)(specific heat of substance)Δt = heat heat = 1638 J mass = 125 g Δt = 52.6 o C – 25.0 o C = 27.6 o C

Calculate the specific heat of a solid in J/g o C and in cal/ g o C if 1638 J raise the temperature of 125 g of the solid from 25.0 o C to 52.6 o C. Convert joules to calories using cal/4.184 J

Example 2

A sample of a metal with a mass of 212 g is heated to o C and then dropped into 375 g of water at o C. If the final temperature of the water is 34.2 o C, what is the 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 (34.2 o C) no net flow of heat occurs.

A sample of a metal with a mass of 212 g is heated to o C and then dropped into 375 g of water at o C. If the final temperature of the water is 34.2 o C, what is the specific heat of the metal?  Calculate the heat gained by the water.  Calculate the final temperature of the metal.  Calculate the specific heat of the metal.

A sample of a metal with a mass of 212 g is heated to o C and then dropped into 375 g of water at o C. If the final temperature of the water is 34.2 o C, what is the specific heat of the metal? Δt = 34.2 o C – 24.0 o C = 10.2 o C temperature rise of the water Heat Gained by the Water heat gained by the water = heat lost by the metal

A sample of a metal with a mass of 212 g is heated to o C and then dropped into 375 g of water at o C. If the final temperature of the water is 34.2 o C, what is the specific heat of the metal? Δt = o C – 34.2 o C = 90.8 o C temperature 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 (34.2 o C).

A sample of a metal with a mass of 212 g is heated to o C and then dropped into 375 g of water at o C. If the final temperature of the water is 34.2 o C, what is the specific heat of the metal? specific heat of the metal = The heat lost or gained by the system is given by: (mass) (specific heat) (Δt) = energy change rearrange

Energy in Chemical Changes

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

Energy Release From Chemical Sources Type of EnergyEnergy Source ElectricalStorage batteries LightA lightstick. Fuel combustion. Heat and LightCombustion of fuels. BodyChemical changes occurring within body cells.

Chemical Changes Caused by Absorption of Energy Type of EnergyChemical Change Electrical Electroplating of metals. Decomposition of water into hydrogen and oxygen LightPhotosynthesis in green plants.

Conservation of Energy

An energy transformation occurs whenever a chemical change occurs.  If energy is absorbed during a chemical change, the products will have more chemical potential energy than the reactants. If energy is given off in a chemical change, the products will have less chemical potential energy than the reactants.

4.4 H 2 + O 2 have higher potential energy than H 2 O energy is given offenergy is absorbed Electrolysis of WaterBurning of Hydrogen in Air higher potential energylower potential energy

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