Physical vs. Chemical Changes
Ice melts into water. What type of change is this?
Physical — no new substance forms.
When two clear liquids are combined, bubbles appear. What type of evidence is this?
Gas Production
Which type of element is typically solid, shiny, and a good conductor of heat and electricity?
Metals
The ability to be drawn into a thin wire is called what?
Ductility
A student mixes clear liquids. One mixture becomes warm, and a white solid forms. What evidence proves a chemical change?
Thermal energy change and formation of a precipitate.
A nail rusts after being left outside. What type of change occurred?
Chemical — new substance (iron oxide) forms.
Evidence: Unexpected Color Change
Two liquids form a yellow solid. What type of evidence shows that a chemical change occurred?
Production of a precipitate.
Which type of element is dull, brittle, and a poor conductor of heat and electricity?
Non-Metals
The ability to be hammered into thin sheets without breaking is called what?
Malleability
Copper turns green and silver turns black when exposed to air. What do these changes have in common, and what causes them?
Both are chemical changes caused by reaction with oxygen (oxidation).
An apple is rotting and smelling stinky. What type of change?
Chemical: New substance formed. Not reversible
Evidence: Color change (Red --> Green/Brown), Change in odor.
A student mixes two powders, and the beaker becomes warm. What evidence of chemical change is shown?
Thermal energy change (temperature increase).
An unknown element is solid, shiny, but only conducts electricity under certain conditions. What type of element is it most likely?
Metalloid
A student observes that sulfur is dull and brittle. What physical property does this describe?
Luster and brittleness (nonmetal traits)
Aluminum, zinc, and copper were placed in acid. Aluminum reached 80°C and formed gas, zinc reached 34°C and changed color, copper stayed the same. Which metals underwent chemical changes? Explain the evidence.
Aluminum and zinc — temperature change, color change, and gas production show chemical reactions.
Sugar dissolves in water. What type of change is this?
Physical --> Can be separated by boiling. Homogeneous or heterogeneous mixtures are physical changes.
When baking a cake, the batter turns brown and produces a sweet smell. What 2 types of evidence is this?
Change in Color/Change of odor
A student compares two elements. Element A is malleable and conducts heat well. Element B is dull and brittle. Which is the metal and which is the nonmetal, and what evidence supports this?
Element A = metal (malleable/conductive);
Element B = nonmetal (dull/brittle).
Which property describes how easily electricity passes through a material?
Conductivity
A scientist adds an unknown element to water. The temperature rises, bubbles form, and the solution becomes cloudy. What type of change is this? What is the evidence, if any?
Chemical Change
Evidence: Thermal energy change, Gas production
Fireworks exploding in the sky on the Fourth of July? What type of change is this?
Chemical: Cannot reverse or undo a firework.
Evidence: Unexpected color change
A metal is placed in an acid, and bubbles form while the metal surface changes from silver to black.
What two pieces of evidence of chemical change are shown?
Gas production and color change.
In an experiment, Element X is lustrous, brittle, and slightly conductive. Element Y is dull, brittle, and does not conduct electricity. Identify each element type and explain your reasoning.
Element X = metalloid (shiny and somewhat conductive);
Element Y = nonmetal (dull, poor conductor).
Look at the periodic table:
Compare copper and sulfur. How do their physical properties differ?
Copper is a metal (lustrous, malleable, conductive); Sulfur is a non-metal (dull and brittle.)
Two clear solutions are mixed.
Solution A becomes yellow and warm.
Solution B remains clear and cool.
Compare and contrast both reactions using the four evidences of chemical change.
Only the first shows a chemical change — a color change and a change in thermal energy indicate the formation of a new substance; the second shows no new evidence.