the characteristics (properties) that can be observed without changing the identity of a substance
Examples of physical properties
mass, color, size, volume, texture, density, state of matter, boiling point, melting point
the ability to dissolve in another substance *Sugar dissolves in water
ability to be drawn into a thin wire *Copper is often used to make wires
ability to be pounded into thin sheets Aluminum can be pounded into sheets to make foil Think of a MALLET
the relationship between the mass and volume of a substance. -We use this to say how much stuff is in a given space.
Formula for Density
Density= mass/volume D = m/v
Density of Water
a change in the physical property of a substance, but DOES NOT change the identity of the substance.
Examples of physical changes
Crumpling a piece of paper, coloring on a piece of paper, freezing water DO NOT GET SOMETHING NEW!
describes how substances can form new substances •Examples: combustibility (how well something can burn), ability to rust/tarnish, cooking
the change of one substance into another substance.
Signs/examples of a chemical change
•Production of odor •Think rotten egg •Burning wood •Silver tarnishing •Cooking (think of an egg) •Rusting/tarnishing •Formation of bubbles Example: antacid tablet in water •Formation of a solid (precipitate) Example: clam shells •Change in temperature •Change in color *Example: iron to rust
How can you tell if a chemical change has occurred?
A new substance is produced!
• What happens to the particles of a substance during a change of state? (think about what changes happen to the particles)
The arrangement of particles The amount of space between particles *The energy of the particles
• Is a change of state a chemical or physical change?
• Know difference between evaporation and boiling
Boiling: vaporization that occurs throughout a liquid -Particles inside the liquid change to a gas and travel to the surface of the liquid and into the air (the bubbling you see in a boiling substance) -Boiling point: the temperature at which a substance boils -Boiling point of substances vary •Boiling point of water (H2O): 100 °C (212 °F) •Boiling point of Mercury (Hg): 357°C (674.6 °F) -For a substance to boil, energy must be absorbed Evaporation: vaporization that occurs at the SURFACE (top) of a liquid •Usually occurs at the surface -This is because the fastest moving particles are at the surface -Evaporation increases as temperature increases •Occurs are a wide range of temperatures (hence why water in a glass disappears after several days)
How does boiling happen?
-Particles inside the liquid change to a gas and travel to the surface of the liquid and into the air (the bubbling you see in a boiling substance)
the change of state from a solid to a liquid
the lowest temperature at which a substance begins to melt
the process by which a liquid becomes a solid
the temperature at which a liquid becomes a solid -Freezing points of substances vary
vaporization (define, types)
the change of state from a liquid to a gas Two types of vaporization: boiling and evaporation
the change of state from a gas to a liquid
temperature at which a gas becomes a liquid
the change of state from a solid directly to a gas -Dry ice is frozen carbon dioxide
Compare freezing/melting point
-The freezing point is the SAME as the melting point! *Freezing is the reverse process of melting, so freezing AND melting occur at the SAME TEMPERATURE -For a substance to melt, energy must be absorbed. -For a substance to freeze, energy must be removed
Compare vaporization (or boiling)/condensation point
*Vaporization is the reverse process of condensation, so vaporization AND condensation occur at the SAME TEMPERATURE -For a substance to condense, energy must be removed. -For a substance to boil, energy must be absorbed.
• Why is evaporation considered a cooling process?
-As a substance evaporates, it absorbs or carries heat away from a surface (hence why sweating cools you off on a hot day)
• Why does a substance boil at a different temperature at different altitudes?
*Pressure affects the boiling point •Water only boils at 100°C at sea level because of atmospheric pressure -Atmospheric pressure is caused by the weight of the gases that make up that atmosphere -Atmospheric pressure is lower at higher elevations (higher you go, less air is above you, and the lower the atmospheric pressure is) -Boil water on a mountain, the boiling point will be lower (example: Denver CO is 1.6 km (1 mile) and water boils at 95°C)
vaporization that occurs throughout a liquid, -Particles inside the liquid change to a gas and travel to the surface of the liquid and into the air (the bubbling you see in a boiling substance) -Boiling point: the temperature at which a substance boils -Boiling point of substances vary
the temperature at which a liquid boils at sea level
vaporization that occurs at the SURFACE (top) of a liquid •Usually occurs at the surface -This is because the fastest moving particles are at the surface -Evaporation increases as temperature increases •Occurs are a wide range of temperatures (hence why water in a glass disappears after several days)
How can you identify an unknown substance?
Can measure/observe physical properties (color, odor, texture, density, boiling point, freezing point) This information MIGHT be enough to tell you the liquid is milk (rather than glue) *Basically, you would compare information of known substances to the information gathered about your unknown
Can you identify an unknown substance by only using mass?
NO! Many objects can have the same mass *Example: 1 kg of M&M's = 1 kg of Skittles
What physical properties can help identify an unknown substance?
density, electric properties, heating properties, magnetic properties, solubility
Give 3 examples of what you might use to separate a mixture.
You can use properties of substances to tell them apart •Example: use a magnet to tell the difference between aluminum and steel •A filter can separate a solid from a liquid •You can use evaporation to separate a liquid that has a solid dissolved in it. (salt water)
Reasons for separating mixtures
Water treatment center •Separates solids from water •Takes chemicals out of water •Disinfects the water •Makes the water safe to drink!
Which is more soluble in water: dirt or salt?
Salt is more soluble since it dissolves in water. Dirt does not dissolve in water.
Electricity flows through some substances (copper) and does not flow through others (rubber, plastic).
Heat travels through some substances easily. Examples: Metals! (iron, aluminum, nickel) •Heat does not travel through some substances very easily. Examples: Plastics, wood, rubber!
Is it possible for two different substances to have the same density?
What is the density of water?
What is the freezing point/melting point of water?
What is the boiling point/condensation point of water?
100 °C (212 °F)