Physical and Chemical Changes & Properties of Matter

Transcription

1 Physical and Chemical Changes & Properties of Matter S8P1. Obtain, evaluate, and communicate information about the structure and properties of matter. 8P1CD Physical And Chemical Properties And Changes c. Plan and carry out investigations to compare and contrast chemical (i.e., reactivity, combustibility) and physical (i.e., density, melting point, boiling point) properties of matter. d. Construct an argument based on observational evidence to support the claim that when a change in a substance occurs, it can be classified as either chemical or physical. (Clarification statement: Evidence could include ability to separate mixtures, development of a gas, formation of a precipitate, change in energy, color, and/or form.)

2 Key Concept 1 The physical properties of matter are measured without changing a substance s chemical identity. Extensive physical properties such as mass, weight, volume, and density, depend on the amount of matter. Intensive physical properties such as freezing/melting point, boiling point, conductivity, do NOT depend on the amount of matter.

3

4 Physical Properties of Matter Physical properties of matter include properties that are measured or described without changing the substance s chemical identity such as viscosity, color, melting point, smell, boiling point, or density. Measuring physical properties will not alter or change the chemical nature of substance because no bonds within the molecules would be broken. Physical properties of a substance can be categorized as either an intensive property or an extensive property:

5 EXTENSIVE Physical Properties Extensive physical properties are physical properties of matter that depend on the amount of matter found within a substance. The amount of matter may be represented by mass, number of particles, or the amount of energy within the substance. Extensive properties include:

6 EXTENSIVE Physical Properties Mass a measurement of the amount of matter in a object measured on a balance scale in units of grams. Weight a measurement of the gravitational force of attraction of Earth acting on an object measured by a spring scale in units of newtons. Volume a measurement of the amount of space a substance occupies. Liquid volume is measured in units of liters using a graduated cylinder or beaker; solid volume is measured using units of cubic meter or cubic centimeters. Length, Width, Height measurements of linear dimensions in units of meters.

7 INTENSIVE Physical Properties Intensive physical properties are physical properties of matter that do not depend on the amount of matter found within a substance. Instead, intensive properties depend on the type of matter found within a substance and are represented by properties such as:

8 INTENSIVE Physical Properties Color (example: sulfur is yellow, while the carbon in coal is black). Odor the smell of a substance such as musty, sweet, pungent, etc. (example: hydrogen sulfide smells like rotten eggs). Luster how shiny a substance is or its reflectivity (example: metals are shiny, while baking soda is dull). Crystal shape the geometric form of a solid substance (example: quartz crystals are shaped like hexagonal prisms). Malleability the ability of a substance to be beaten into thin sheets (example: the malleability of gold allows it be formed into thin sheets called gold leaf ). Ductility the ability of a substance to be drawn into thin wires (example: the ductility of copper makes it a common metal used as wire). Conductivity the ability to allow flow of thermal energy or electricity (example: metals are good conductors of both heat and electricity).

9 INTENSIVE Physical Properties Hardness how easily a substance can be scratched (example: the mineral talc is so soft it can be scratched with a fingernail, while diamond is so hard you can only cut it with another diamond). Solubility how easily a substance can dissolve in water (example: sugar dissolved in water). Magnetism the ability to attract iron (example: magnetite and lodestone are naturally magnetic). Melting/Freezing Point the temperature at which a solid becomes liquid and when a liquid becomes a solid; measured in degrees Celsius (example: water has a melting/freezing point of 0 Celsius). Boiling Point the temperature at which a liquid turns into gas (example: water has a boiling point of 100 o Celsius). Density the amount of matter per unit of volume measured in g/cm 3 (example: metals are denser than plastics).

10 Key Concept 2 Key Concept 2: The chemical properties of matter, such as combustibility and reactivity, are measured only by changing a substance s chemical identity.

11

12 Chemical Properties of Matter A chemical property defines whether a chemical reaction will or will not take place. Chemical properties of matter include all of the possible chemical changes that a sample of matter can undergo. Scientists use chemical properties to predict whether a sample will have a certain chemical reaction. Chemical properties include:

13 Chemical Properties of Matter Flammability ability to ignite in the presence of a flame. Example: Wood and paper are highly flammable, while rocks are not. Ability to oxidize ability to gain oxygen, lose hydrogen, or gain electrons. Example: Iron corrodes into rust easily. Reactivity to water produces bubbles or explodes in the presence of water. Example: Alkali metals react violent with water. Heat of combustion the amount of heat released when a substance is burned. Example: Some woods are denser and burn at much higher temperatures than other woods. ph reactivity with water to see how acidic or basic a substance is. Example: Citric juices are very acidic (have a low ph) while detergents are very basic (have a high ph).

14 Key Concept 3 A physical change to matter will not alter the composition or identity of a substance, while a chemical change to matter will always result in the formation of a new substance often marked by a color change, formation of gas, precipitates, temperature change, etc.

15

16

17 Physical Changes include: Changing the shape of a substances such a folding, cutting, bending, crushing, sanding, stretching, breaking, etc. For example, cutting, sanding, or sawing wood only changes the shape of the wood, but it does not change the composition of the wood. Changing the state of matter such as melting, freezing, boiling, condensing, evaporating, or subliming. For example, change of state involves changing the motion of the particles contained in the matter. Going from solid to liquid increases the distance between the atoms but does not change the chemical composition of the matter. Changing the color of matter by painting. For example, painting a metal fence does not change the composition of the metal.

18 Chemical Changes When a chemical change occurs, new substances are formed. Elements or compounds may also recombine to form new compounds. In all of these types of changes, new substances with new properties form. Various types of evidence are used to identify the formation of a new substance through a chemical change:

19

20 Evidence of Chemical Change Production of Gas: Gas production is a form of evidence indicating a chemical change taking place. For example, when baking soda and vinegar react, one of the products formed is carbon dioxide gas. When the two reactants combine, bubbles may be seen indicating the production of CO 2. Not all gas production results from a chemical change. The bubbles from opening a carbonated beverage are merely a physical change that occurs when pressure is released.

21 Evidence of Chemical Change Temperature Change: Changes in temperature are sometimes used as evidence to indicate a chemical reaction has occurred. Temperature change, however, does not always indicate a chemical change. Thermal energy is transferable in many processes, including physical changes. For instance, when ice is placed in warm water, the temperature changes but no chemical reaction takes place. A temperature change does indicate a chemical reaction when two substances with similar beginning temperatures are combined and either produce heat (an exothermic reaction) or lose heat (an endothermic reaction).

22 Evidence of Chemical Change Precipitate Forms: The formation of a precipitate can be evidence of a chemical change. A precipitate is an insoluble compound formed out of a solution. A common example of precipitate formation is seen when mixing two clear solutions, silver nitrate and sodium chloride. The result is a chemical change in which two products (liquid sodium nitrate and silver chloride) produce a white solid. Silver chloride is the precipitate.

23 Evidence of Chemical Change Change of Color: Color changes, as with temperature changes, are sometimes used as evidence of a chemical change. Not all color changes indicate chemical changes. For example, adding food color to water might appear to change the color of the water, but no chemical reaction takes place. A color change that is evidence of a chemical change happens when two clear solutions, silver nitrate and potassium iodide are mixed, a bright yellow compound called silver iodide precipitates. This color change is an indicator of a chemical change, as well as a sediment formation.

24 Evidence of Chemical Change Production of Light: When a substance rapidly combines with oxygen, combustion occurs and a flame is produced that gives off thermal energy and light. Burning paper or wood produces light. In some chemical reactions, such as mixing the chemicals in a Glow Stick - a fluorescent light can be produced.