Chemeketa Community College Properties of Matter Chapter 4 Larry Emme Chemeketa Community College

Properties of Substances

Properties of a Substance A property is a characteristic of a substance. Each substance has a set of properties that are characteristic of that substance and give it a unique identity.

Physical Properties

The inherent characteristics of a substance that are determined without changing its composition. Examples: taste color physical state melting point boiling point density

Physical Properties of Chlorine 2.4 times heavier than air color is yellowish-green odor is suffocating or sharp melting point –101oC boiling point –34.6oC

Chemical Properties

Describe the ability of a substance to form new substances, either by reaction with other substances or by decomposition.

Chemical Properties of Chlorine It will not burn in oxygen. It will support the combustion of certain other substances. It can be used as a bleaching agent. It can be used as a water disinfectant. It can combine with sodium to form sodium chloride.

Physical Changes

Physical Changes Changes in physical properties (such as size shape and density) or changes in the state of matter without an accompanying change in composition. Examples: tearing of paper change of ice into water change of water into steam heating platinum wire

Chemical Changes

In a chemical change new substances are formed that have different properties and composition from the original material. yields + Na Cl2 NaCl

Formation of Copper(II) Oxide 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. 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 20.1% oxygen by mass.

Formation of Copper(II) Oxide Neither Cu nor O2 contains Cu2+ or O2- Copper(II) oxide is made up of Cu2+ and O2- A chemical change has occurred.

Chemical Equations

Chemical symbols can be used to express chemical reactions

Copper plus oxygen yields copper(II) oxide. heat reactants product yield

Conservation of Mass

No change is observed in the total mass of the substances involved in a chemical change.

sodium + sulfur  sodium sulfide → 46.0 g 32.1 g 78.1 g 78.1 g reactant 78.1 g product mass reactants = mass products

Heat: Quantitative Measurement

A form of energy associated with small particles of matter. Heat A measure of the intensity of heat, or of how hot or cold a system is. Temperature

Units of Heat Energy

(exactly) 4.184 Joules = 1 calorie The SI unit for heat energy is the joule (pronounced “jool” rhymes with fool). Another unit is the calorie. 4.184 J = 1 cal (exactly) 4.184 Joules = 1 calorie This amount of heat energy will raise the temperature of 1 gram of water 1oC.

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 1oC.

Specific Heat of Substances Specific heat (cal/gC) Water 1.00 Ethyl alcohol 0.511 Ice 0.492 Steam 0.481 Iron 0.113 Copper 0.0921 Gold 0.0312 Lead 0.0305

The units of specific heat in calories are:

The relation of mass, specific heat, temperature change (ΔT), and quantity of heat lost or gained is expressed by the general equation: Heat (cal) = mass (g)  specific heat (cal/g C)  ΔT (C)

Example

Calculate the specific heat of a solid in cal/goC if 391 Calculate the specific heat of a solid in cal/goC if 391.5 cal raise the temperature of 125 g of the solid from 25.0oC to 52.6oC. heat = (mass)(specific heat)Δt heat = (g)(specific heat)Δt heat = 391.5 cal mass = 125 g Δt = 52.6oC – 25.0oC = 27.6oC 391.5 cal 0.113 cal g C =

Energy in Chemical Changes

In all chemical changes, matter either absorbs or releases 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 by Absorption of Energy Type of Energy Chemical Change Electrical Electroplating of metals. Decomposition of water into hydrogen and oxygen Light Photosynthesis in green plants.

The End