Notes on Physical and Chemical Changes

09/09/11Notes on Physical and Chemical ChangesMaking ObservationsQuantitative

Qualitative

What is the difference between these terms?Making ObservationsQuantitative - The word quantitative means "of, relating to, or expressible in terms of quantity," according to Merriam-Webster's Dictionary. Simply put, quantitative observations are those in which the focus is the numbers. Examples are "the object is moving at 4 meters per sec", "all volumes doubled in size", or "the pressure was increased to 3 atmospheres".

Qualitative - Qualitative observations are those that provide a sense of observed parameters or changes without reference to numerical or statistical values. Qualitative observations have more to do with characteristics of what is being observed. Examples are "A heated filament glows." "The chemical turns red." "One rod is longer.

We used observations to identify Properties

Physical PropertiesAny characteristic of a material that can be observed or measured without changing the composition of the substance in the materialPhysical PropertiesAny characteristic of a material that can be observed or measured without changing the composition of the substance in the materialExamples are: viscosity, conductivity, malleability, hardness, density, and boiling/melting/freezing points.Comparing Intensive vs. Extensive PropertiesIntensive Properties that do not depend on the amount of matter present.Comparing Intensive vs. Extensive PropertiesIntensive Properties that do not depend on the amount of matter present.Examples include: Color, odor, luster, malleability, ductility, conductivity, hardness, melting/freezing point, boiling point, densityComparing Intensive vs. Extensive PropertiesIntensive Properties that do not depend on the amount of matter present.Examples include: Color, odor, luster, malleability, ductility, conductivity, hardness, melting/freezing point, boiling point, density

Extensive - Comparing Intensive vs. Extensive PropertiesIntensive Properties that DO NOT depend on the amount of matter present.Examples include: Color, odor, luster, malleability, ductility, conductivity, hardness, melting/freezing point, boiling point, density

Extensive Properties that DO depend on the amount of matter presentExamples include: mass, weight, volume, length, width, height, amount of energy in the substance, number of moles

Physical ChangesA change where the substance of the material remains the sameExamples: Braiding and unbraiding hairSlicing an appleMelting butterBoiling waterCutting hairIroning a shirt to remove wrinkles

Why is this a physical change?

Why is this a physical change?

Chemical PropertiesA characteristic that produces a change in the composition of matterChemical PropertiesA characteristic that produces a change in the composition of matterExamples: flammability (the ability to burn) and reactivity (how easily a substance combines chemically with other substances)Chemical ChangesA change in matter that PRODUCES A NEW SUBSTANCE. In order for this to occur, a reaction has to occur.

We look for evidence of a change by looking for a few signs that a reaction has taken place.Signs of Chemical ChangesA change in colorIron has reacted with oxygen

Signs of Chemical ChangesA change in colorThe production of a gasAn acid reacts with an antacid

Signs of Chemical ChangesA change in colorThe production of a gasFormation of a precipitate (a solid formed when combining two liquids)

Lead iodide is the yellow solid formed and potassium nitrate is the liquid in the beaker

Signs of Chemical ChangesA change in colorThe production of a gasFormation of a precipitate (a solid formed when combining two liquids)Heat is given off or absorbed

Signs of Chemical ChangesA change in colorThe production of a gasFormation of a precipitate (a solid formed when combining two liquids)Heat is given off or absorbedLight is emitted

Signs of Chemical ChangesA change in colorThe production of a gasFormation of a precipitate (a solid formed when combining two liquids)Heat is given off or absorbedLight is emittedChange in smell or tasteSmells bad

Tastes bad