Matter And Energy Chemistry Ch 3

The Nature of Matter Gold Mercury Chemists are interested in the nature of matter and how this is related to its atoms and molecules.

Chemistry & Matter We can explore the MACROSCOPIC world — what we can see — to understand the PARTICULATE worlds we cannot see. We write SYMBOLS to describe these worlds.

A Chemist’s View of Water Macroscopic H2O (gas, liquid, solid) Symbolic Particulate

A Chemist’s View Macroscopic 2 H2(g) + O2 (g) --> 2 H2O(g) Particulate Symbolic

Kinetic Nature of Matter Matter consists of atoms and molecules in motion.

STATES OF MATTER SOLIDS — have rigid shape, fixed volume. External shape can reflect the atomic and molecular arrangement. Reasonably well understood. LIQUIDS — have no fixed shape and may not fill a container completely. Not well understood. GASES — expand to fill their container. Good theoretical understanding.

OTHER STATES OF MATTER PLASMA — an electrically charged gas; Example: the sun or any other star BOSE-EINSTEIN CONDENSATE — a condensate that forms near absolute zero that has superconductive properties; Example: supercooled Rb gas

Physical Properties What are some physical properties? color melting and boiling point odor

Physical properties of matter are categorized as either Intensive or Extensive: Intensive - Properties that do not depend on the amount of the matter present. Color Odor Luster - How shiny a substance is. Malleability - The ability of a substance to be beaten into thin sheets. Ductility - The ability of a substance to be drawn into thin wires. Conductivity - The ability of a substance to allow the flow of energy or electricity. Hardness - How easily a substance can be scratched. Melting/Freezing Point - The temperature at which the solid and liquid phases of a substance are in equilibrium at atmospheric pressure. Boiling Point - The temperature at which the vapor pressure of a liquid is equal to the pressure on the liquid (generally atmospheric pressure). Density - The mass of a substance divided by its volume

Physical properties of matter are categorized as either Intensive or Extensive: Extensive - Properties that do depend on the amount of matter present. Mass - A measurement of the amount of matter in a object (grams). Weight - A measurement of the gravitational force of attraction of the earth acting on an object. Volume - A measurement of the amount of space a substance occupies. Length

Physical Changes Some physical changes would be boiling of a liquid can be observed without changing the identity of the substance Some physical changes would be boiling of a liquid melting of a solid dissolving a solid in a liquid to give a homogeneous mixture — a SOLUTION.

Chemical Properties and Chemical Change Burning hydrogen (H2) in oxygen (O2) gives H2O. Chemical change or chemical reaction — transformation of one or more atoms or molecules into one or more different molecules.

Sure Signs of a Chemical Change Heat Light Gas Produced (not from boiling!) Precipitate – a solid formed by mixing two liquids together

Physical vs. Chemical physical Examples: melting point chemical flammable density magnetic tarnishes in air

Physical vs. Chemical chemical Examples: rusting iron physical dissolving in water burning a log melting ice grinding spices

Can it be physically separated? Matter Flowchart MATTER yes no Can it be physically separated? MIXTURE PURE SUBSTANCE Is the composition uniform? no yes Can it be chemically decomposed? no yes Homogeneous Mixture (solution) Heterogeneous Mixture Compound Element Colloids Suspensions

Types of Mixtures Variable combination of 2 or more pure substances. Heterogeneous – visibly separate phases Homogeneous – Same throughout

Alloys

Law of Definite Proportions Joseph Proust (France 1799) A given compound always contains elements in a certain proportion by mass. (Constant composition).

Percent Mass of Compounds Atoms combine in whole number ratios, so their proportion by mass will always be the same. Example: H2O is always made up of 2 atoms of H and one atom of O. The mass ratio of O to H in water is always 16:2 or 8:1. Percent Mass of Compounds Percent composition consists of the mass percent of each element in a compound: Percent by mass=

Example: KCl KCl always contains one atom of K for every one atom of Cl In KCl, potassium and chlorine always have a ratio of “39.09 to 35.45” or “1.1 to 1” by mass.

Law of Multiple Proportions (John Dalton) When the same two elements combine to form more than one compound: the ratios of the mass of one element in the first compound to its mass in the second compound, (as it combines with the same mass of the other element), can always be expressed as ratios of small whole numbers( ex: 1:3 or 2:5).

Example of Law of Multiple Proportions Carbon combines with oxygen to form CO and CO2 . Mass of Carbon(g) Mass of Oxygen(g) Ratio of O in CO2 to O in CO CO CO2 12.01 16.00 2:1 12.01 32.00

Practice Problem 1 Mass of Carbon (g) Mass of Hydrogen (g) In the carbon compounds ethane (C2H6) and ethene (C2H4), what is the lowest whole number ratio of H atoms that react with the same number of C atoms? Mass of Carbon (g) Mass of Hydrogen (g) Ratio of H in C2H6 to H in C2H4 C2H6 C2H4 24.02 6.06 6:4 or 3:2 24.02 4.04