Properties of Matter. Properties. Physical Properties 8/14/2011. Chapter 4

Transcription

1 Properties of Matter Chapter 4 Properties What is the function of properties? ANSWER: It is characteristics which can be used to identify a substance. QUESTION: What type of properties exist in any chemical substance? Physical Properties Characteristics which demonstrates a change in the state of matter, not in composition. EXAMPLES: 1. Density 5. Taste 2. Melting Point 6. Color 3. Boiling Point 7. Odor 4. Appearance 1

2 Physical Properties of Chlorine 2.4 times heavier than air color is yellowish-green odor is disagreeable melting point 101 o C boiling point 34.6 o C 4 Chemical Properties Characteristics which allows a substances to change its composition. This may or may not result in a change in state between the reactant(s) and products. EXAMPLES: 1. Corrosiveness 5. Flammability 2. Acidity 6. Oxidizability 3. Toxicity 7. Reactivity (water) 4. Basicity Chemical Properties of Chlorine Itwillnotburninoxygen. It will support the combustion of certain other substances. Itcanbeusedasableachingagent. Itcanbeusedasawaterdisinfectant. It can combine with sodium to form sodium chloride. 6 2

3 REFERENCE Properties of Substances When chemists need to look for information for any substance, one of the most common reference books we use is the CRC Handbook of Chemistry and Physics!!! Concept Check Which is not a physical property of aluminum? a. Aluminum is silver and has luster. b. The melting point of aluminum is 660 º C. c. Aluminum reacts with acid to produce an aluminum salt and hydrogen gas. d. The density of aluminum at 25 º C is 2.70 g/cm 3. 3

4 Concept Check Which characteristic about acetone is a chemical property? a. The specific gravity of acetone is b. The boiling point of acetone is 56 C. c. Acetone is a clear, colorless liquid. d. Acetone is a flammable liquid. Physical Changes A physical change involves changes in physical properties (i.e. size, shape and density) or a change in the state of matter without a change in composition. EXAMPLE: Figure 1 A bowl of liquid water being heated into water vapor. H 2 O (l) H 2 O (g) Chemical Changes A chemical change involves a transformation not only in appearance, but in matter!!! Figure 2- (a) Initially, 100% copper (1.000 gram). (b) Copper and oxygen are reacting with each other. (c) After the reaction is completed, copper (II) oxide is produced comprising of 79.9% copper and 20.0% oxygen. 4

5 Chemical Changes Figure 3-Electrolysis of water with hydrogen gas(right) and oxygen gas(left). Chemical Changes ALL chemical changes must be supported by writing a chemical equation. A chemical equation can be expressed in one of three ways: 1. Word 2. Molecular 3. Symbol (FORMULA) Let s look at the hydrolysis of water!!! Figure 4-Illustration of writing equations for the decomposition of water. 5

6 Figure 5-Illustration of writing equations for the synthesis of copper(ii) oxide. Concept Check Chemical changes always involve changes in which of the following? a. Chemical composition b. Physical properties c. Chemical properties d. All of the above Concept Check Which is a chemical change? A. Corrosion of steel B. Freezing water C. Evaporating gasoline D. Forming fog 6

7 Chemical Reactions There are two sides to a chemical reaction. The starting substances written on the left side of a chemical reaction is called the reactants. Symbols = heat (s)= solid (l)= liquid (g) = gas (aq) = aqueous state The ending substances written on the right side of a chemical reaction is called the products. Chemical Change w/physical Change All chemical changes are usually accompanied by a physical change. Some common physical changes observed can include any combination of the following changes: 1. Color 2. Solid 3. Size of Substance 4. Odor 7

8 Law of Conservation of MASS This law states that there is no change in mass observed within a chemical reaction. MASS of reactants = MASS of products EXAMPLE: The decomposition of potassium chlorate results in potassium chloride and oxygen. potassium chlorate potassium chloride + oxygen Example Law of Conservation of MASS potassium chlorate potassium chloride + oxygen If there is grams of reactant, there MUST be grams of product for this law to be VALID!!! If there are 39.1 grams of oxygen produced, what mass of potassium chloride must have been produced? ANSWER: What is energy? Energy It is the capacity of matter to perform work. Let s look at examples of types of energy!!! 8

9 TYPES of Energy Some of most familiar forms of energy include the following: 1. Potential Energy 2. Kinetic Energy 3. Mechanical Energy 4. Electrical Energy 5. Heat 6. Nuclear Energy 7. Light Energy Potential ENERGY This form of energy is energy which is stored in an object in its relative position. EXAMPLES: A boulder is positioned at the top of the hill 50 feet from the ground. Gasoline is in a gas tank in an automobile is still has potential energy until it is burned with oxygen gas. Kinetic ENERGY This form of energy is one which is present in matter via motion. EXAMPLES: A moving body. A moving automobile. A walking robot. A sprint runner. 9

10 Heat Heat is another form of energy which is associated with the motion of the matter. Common Equalities: J = 1 cal 1 kj = 1000 J 1 kcal = 1000 cal = 1 Cal NOTE: all of these equalities have infinite SF. Units of Energy Recall the SI unit of energy is Joule (J). Other common units are calorie (cal) and kcal (kcal). Is heat and temperature the same in meaning!!! ANSWER: Differences Heat vs. Temperature Remember, temperatureis a measure of the intensity of heat (Kelvin, Celsius or Fahrenheit). However, heatis a form of energy which associates the motion of the molecules of the matter. Let s look at an example illustrating the differences!!! 10

11 Differences Heat vs. Temperature A system containing two beakers. Both contains water. Beaker A = 100. g and Beaker B = 200. g BEAKER A (20-30 o C) E= 4184 J BEAKER B (20-30 o C) E= 8368 J QUESTION: What do you recognize is the relationship between mass and energy? Specific Heat DEVELOPMENT Now, when performing studies involving different substances, it was the focus of Scottish chemist, Joseph Black ( ). IRON LEAD Specific Heat DEVELOPMENT (cont d) RECALL: J = 1 cal Black found is that each substance has their own physical property (a specific heat capacity). A specific heatcapacity of a substance is the quantity of heat (lost or gained) for the substance to increase or decrease 1 g of that substance per 1 o C. LET S for the table for some specific heat capacities for different substances. 11

12 Specific Heat Capacities Calculating ENERGY When one wants to calculate the amount of energy being released or absorbed, one can do that using the following equation: Energy = m S t MASS Temperature Change Specific Heat ENERGY Calculations Question: How much energy is present in 50.0-g sample of water when the system s temperature increases from 24.5 o C to 36.0 o C? 12

13 ENERGY Calculations PRACTICE 4.2 A g sample of metal at 55.5 o C raises the temperature of g of water from 23.0 o C to 25.5 o C. Determine the specific heat of the metal in J/g o C. Energy Release From Chemical Sources Type of Energy Electrical Light Heat and Light Body Energy Source Storage batteries A lightstick. Fuel combustion. Combustion of fuels. Chemical changes occurring within body cells. 38 Chemical Changes Caused by Absorption of Energy Type of Energy Electrical Light Chemical Change Electroplating of metals. Decomposition of water into hydrogen and oxygen Photosynthesis in green plants

14 Law of Conservation of Energy The law of conservation of energy states that energy is neither created or destroyed. Let s look at the example of the synthesis and decomposition of water!!! higher energy potential is absorbed energy lower energy potential is given energy off EQUATION: H 2 O + energy = > H 2 + O 2 EQUATION: H 2 + O 2 = > H 2 O + energy Figure 6-An illustration of the synthesis and decomposition of water. Additionally equations of these processes are shown below!!! Concept Check Which of the following processes result in the system losing energy and having negative energy values? a. arctic ice melting b. dry ice changing to vapor c. starting a car d. dynamite exploding 14

15 Concept Check Which of the following physical changes does not require energy to take place? a. Evaporation b. Melting c. Condensation d. Sublimation ENERGY-Real World Chemical reactions in the sun produce the heat and light our planet needs to survive. Plants use photosynthesis to store energy from the sun. Plants decay and eventually produce fossil fuels (after millions of years). We burn fossil fuels to perform work. Energy-Fossil Fuels Petroleum is composed of hydrocarbons. Natural gas is usually a mixture of methane with small amounts of ethane propane and butane. Coal is essentially carbon. It provides roughly 20% of US energy needs. 15

16 Exploration of OTHER Resources 16