Chapter Outline 4.1 Properties of Substances 4.2 Physical Changes 4.3 Chemical Changes 4.4 Conservation of Mass 4.5 Energy 4.6 Heat: Quantitative Measurement 4.7 Energy in Chemical Changes 4.8 Conservation of Energy
In a chemical change new substances are formed that have different properties and composition from the original material.
Formation of Copper(II) Oxide Heating a copper wire in a Bunsen burner causes the copper to lose its original appearance and become a black material. The black material is a new substance called copper(II) oxide. Copper is 100% copper by mass. Copper (II) oxide is: 79.94% copper by mass and 20.1% oxygen by mass. The formation of copper(II) oxide from copper and oxygen is a chemical change. The copper (II) oxide is a new substance with properties that are different from copper.
Formation of Copper(II) Oxide Copper(II) oxide is made up of Cu 2+ and O 2- Neither Cu nor O 2 contains Cu 2+ or O 2- A chemical change has occurred. 4.2
Water is decomposed into hydrogen and oxygen by passing electricity through it. Decomposition of Water The composition and physical appearance of hydrogen and oxygen are different from water. The hydrogen explodes with a pop upon the addition of a burning splint. The oxygen causes the flame of a burning splint to intensify. They are both colorless gases. But the burning splint is extinguished when placed into the water sample.
The SI unit for heat energy is the joule (pronounced “jool”).
Another unit is the calorie.
This amount of heat energy will raise the temperature of 1 gram of water 1 o C. 4.184 J = 1 cal (exactly) 4.184 Joules = 1 calorie
An Example of the Difference Between Heat and Temperature A form of energy associated with small particles of matter. A measure of the intensity of heat, or of how hot or cold a system is.
Twice as much heat energy is required to raise the temperature of 200 g of water 10 o C as compared to 100 g of water. 200 g water 20 o C A 100 g water 20 o C B heat beakers temperature rises 10 o C 100 g water 30 o C 200 g water 30 o C 4184 J 8368 J
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) Δ t = heat (g)(specific heat of substance) Δ t = heat heat = 1638 J mass = 125 g Δ t = 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 1.000 cal/4.184 J
In all chemical changes, matter either absorbs or releases energy .
Energy Release From Chemical Sources Chemical changes occurring within body cells. Body Combustion of fuels. Heat and Light A lightstick. Fuel combustion. Light Storage batteries Electrical Energy Source Type of Energy
Chemical Changes Caused by Absorption of Energy Photosynthesis in green plants. Light Electroplating of metals. Decomposition of water into hydrogen and oxygen Electrical Chemical Change Type of Energy