Physical and Chemical Changes Pure Substances Mixtures States of Matter

Everything that has mass and volume is called matter.

There is no observable change in the quantity of matter during a chemical reaction or a physical change. In other words, matter cannot be created nor destroyed. It is just converted from one form to another

Have a definite shape Have a definite volume Particles of solids are tightly packed, vibrating about a fixed position.

 Have an indefinite shape  Have a definite volume  Particles of liquids are tightly packed, but are far enough apart to slide over one another.

Have an indefinite shape Have an indefinite volume  Particles of gases are very far apart and move freely.

Changing States of Matter

Boiling point and melting point The melting point is the temperature at which a solid turns into a liquid. This is also the freezing point. Ex. At 0ºC ice melts into water and water freezes into ice. The boiling point is the temperature at which a liquid turns into a vapor. This is also the condensation point. Ex. At 100ºC, water boils and becomes vapor and water vapor condenses into liquid.

What are phase changes called? Added heat

All matter, regardless of state, undergoes physical and chemical changes. These changes can be microscopic or macroscopic.

Measuring Matter How can we measure matter? What equipment would we need?

Mass and Weight Are they the same? What happens to our mass and weight if we were to go to the moon? If two substances have the same weight, do they have the same mass?

Measuring Mass Mass: Amount of substance How can we measure mass? Scale or balance What are the units of mass? Grams (or pounds)

Measuring Volume Volume: Amount of space a substance takes up How can we measure (or calculate) volume? measuring cup, graduated cylinder, (ruler) What are the units of volume? mL, L, cm 3, in 3

Water Displacement Volume = change in water level Volume of water with object − volume of water alone If two substances have the same volume, will they displace the same amount of water?

Do We Have Gold? How could we use mass and volume to prove if our golden penny is really gold?

Discover Density Density: How much stuff is in a certain space D= m/V m DV  To determine the density of a substance, divide its mass by its volume.  To solve for volume, divide mass by density.  To solve for mass, multiply density by volume.

 A substance changes state but does not change its chemical composition. For example: water freezing, cutting a piece of wood The form or appearance has changed, but the properties of that substance are the same

 A substance changes into something new.  Occurs due to heating/chemical reaction  The common signs of a chemical change are:  Bubbles forming  Heat is given off, or taken in  Mass changed  Color change emistry/propertychanges/

Physical and chemical properties may be intensive or extensive.

intensive properties do not depend on the size of the sample of matter and can be used to identify substances. Density Color Boiling Point Melting Point

extensive properties DO depend on the quantity of the sample. Mass volume

Physical properties are those that we can determine/observe without changing the identity of the substance we are studying. Examples: Hardness, color, density, melting/boiling point

Chemical properties describe the way a substance can change or react to form other substances. Any of a material’s properties that become evident during a chemical reaction In other words, we have to define chemical properties of a substance by the chemical changes it undergoes…the substance’s internal structure must be altered for these properties to be observed Ex: Heat of combustion, reactivity w/ water

Substances can be identified as either an element, compound, or a mixture.

Compounds Can be decomposed into simpler substances by chemical changes, always in a definite ratio ( combo of two or more elements ) H 2 O ; H 2 O 2  Hydrogen ; Oxygen Elements Cannot be decomposed into simpler substances by chemical changes

Fixed composition Cannot be separated into simpler substances by physical methods Ex: You can’t separate the H from the O in H2O2 without a chemical change Can only be changed in identity and properties by chemical methods Properties do not vary

Mixtures are two or more substances that are NOT chemically combined – Can be separated by physical means or chemical means ( sometimes ) ; i.e. Sieve (physical) or Column Chromatography (chemical) Mixtures do not:  Have constant boiling points  Have constant melting points

Have variable composition Components retain their individual characteristic properties (i.e. Sand/Salt Mixture: sand and salt retain their individual BPs, MPs, etc.) May be separated into pure substances by physical or chemical methods – Mostly PHYSICAL Mixtures of different compositions may have widely different properties EX: imagine a handful of M&Ms as an examples – or … a handful of different types of beans:

Have the same composition throughout Components are indistinguishable Liquid: Looks like a single, uniform liquid Solid: An Alloy – Stainless steel(Iron, Chromium, others…) May or may not scatter light Examples: Kool-Aid, shampoo, etc.

Solutions are homogeneous mixtures that do not scatter light. (exception: COLLOIDS) Created when something is completely dissolved in pure water. Therefore, they are easily separated by distillation or evaporation. Examples: Kool-Aid, salt water

Colloids are solutions. Substance that is microscopically dispersed in another substance They can be described as a substance trapped inside another substance They can be identified by their characteristic scattering of light. For example: jello, fog, smoke, milk, vanilla yogurt Milk  a colloid of liquid butterfat globules dispersed within a water-based solution

Do not have same composition throughout Components are distinguishable Examples: fruit salad, vegetable soup, etc.

Suspensions are mixtures that do not stay mixed The solute settles or can be filtered out Examples: lava lamp, snow globes

Table 2.1 (pg 40) SubstanceStateColorM.P. ( °C) B. P. ( °C) NeonGascolorless OxygenGasColorless ChlorineGasGreenish-yellow EthanolLiquidColorless MercuryLiquidSilvery-white BromineLiquidReddish-brown-759 WaterLiquidColorless0100 SulfurSolidYellow Sodium chlorideSolidWhite GoldSolidYellow CopperSolidReddish-yellow