Stop and Think Pg 87

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Stop and Think Pg 87 1-4

Stop and Think pg 87 1) Which half of the reaction, reactant or product, had a greater mass when you constructed only one molecule each of methane, oxygen, carbon dioxide, and water? Explain why using the correct symbols for each atom and the law of conservation of matter. CH4 + O2 CO2 +H2O Reactant Product The reactant side had more mass (before balanced). That is because 1 methane molecule (CH4) and one oxygen molecule (O2) have a total of 7 atoms, each one about the same mass. Remember, that atoms of different elements have different mass. Most model kits do not model differences in atomic mass. This product side has a total of 6 atoms due to 1 carbon dioxide (CO2), and 1 water molecule (H2O)

Stop and Think pg 87 2) Which molecules did you have to build more of in order to show conservation of matter? Explain how you selected which molecules and how many. One more molecule of oxygen (O2) and that created one more molecule of water in the product (H2O). Once that oxygen molecule was built it produced a second water and the equation was able to obey the law of conservation. All the atoms on the reactant side = all the atoms on the product side

Stop and Think pg 87 3) Explain why the mass of the candle changed after 2 minutes of combustion, considering the law of conservation of matter. The candle lost mass because carbon dioxide was formed (gas) and floated away. We saw from the previous experiment (antacid) that carbon dioxide did indeed have mass (balloon). So when the candle lost carbon [(C4OH4)2] in the form of carbon dioxide it lost mass.

Stop and Think pg 87 4) What steps did you take in the antacid tablet in water reaction that were different from the burning candle reaction in regard to the conservation of matter? Explain why those didn’t work. In the soda bottle reaction we captured all the gas produced from the reaction. In the candle, gas was lost to in the air and dispersed throughout the room. The candle burning was not a closed system

Reacting to Density Pt: III Phases of Matter • I have a few candles lit at the front of the class use those for this investigation • Process and Procedures 1-5 (PLEASE SKIP 3) • You do not need to blow out my candle • You have all seen what a candle looks like when it blows out. • If you would like a demo, I can do it once for the class

Stop and Think pg 89 1-4 Questions and Answers in complete sentences. Due MONDAY!!!! Monday we will finish the chapter Review on Tuesday Test on TUESDAY!!!

Background Info In the investigation we observed TWO chemical reactions: an antacid tablet in water, and a candle burning. In each reaction, some material appeared to be destroyed and other matter will be created. What’s wrong with this idea? Mass is not lost or gained, but merely rearranged at the atomic level! • New molecules are made from existing atoms. • New materials have different properties than the original materials • – the greatest indicator of chemical change. • For instance, shiny aluminum exposed to oxygen turns dull – it gets coated with aluminum oxide. • Liquids USUALLY have lower density (about 10%) than the solid forms but not always (think of water and ice…)

Section Objectives • Defineelement, molecule, compound, chemical change, physical change. • Interpret chemical formulas. • Balance chemical equations. • Explain the differences between compounds and mixtures.

Physical Change • A change where the composition of the substance remains the same, even if the appearance does not. • Examples: changes of state (solid – liquid – gas) • What’s happening at the atomic level?

Chemical Change • Substances are changed into new substances with their own unique properties. • Examples: charcoal burns, iron rusts

Element • A substance made from only one type of atom. • An element cannot be broken down (chemically) into a more simple substance. • Examples: Carbon is made entirely from Carbon atoms. • Sodium is made entirely from Sodium atoms. • But water is H2O… it has TWO elements!

Molecule • A molecule is a neutral group of atoms that are held together by covalent bonds

Compound • A substance that is made of two or more atoms or two or more elements that are chemically bonded. • The compound’s properties are unique to that compound • They do not necessarily maintain the properties to each of the atoms that make up the compound

Diatomic Molecule • Molecules made up of two atoms, which can be the same element. • N2, F2, Cl2, O2.

Chemical Formulas How about CO2? • A combination of symbols and numbers that show which elements, and the number of atoms of each element, that make up a molecule of a compound. The numbers here are called subscripts.

Balanced Equations • The number of atoms of each type must be equal to each other on either side of the arrow. WHY?? • You cannot change the chemical formulas. • We put numbers (called coefficients) in front of the reactants or products to make it balance.

Homogenous Mixtures • Means “having the same composition and properties throughout.” • Also called a solution, in which two or more substances are uniformly dispersed. • Can be solid, liquid, or gas. Smog build-up during the day

Heterogeneous Mixtures • Where two or more substances are not uniformly distributed. Granite, mostly a mixture of orthoclase and quartz.

Background Info ~ Phase Diagrams Phase Diagrams are used to show the regions in which different phases exist in a closed system at equilibrium.

Background Info ~ Phase characteristics Gases are made up of large numbers of very small particles (atoms and molecules). Most of the volume in a gas is empty space. Gas particles are usually ‘far apart’ from one another – in a microscopic sense.  Particles in gases are constantly in motion, and move in straight lines at high speeds until they bump into something, when they ricochet off in another direction (Brownian motion). When gas particles collide, their collisions are “elastic” – no kinetic energy is lost. In general, gas particles do NOT attract or repel each other. The greater the temperature, the greater the kinetic energy and the faster the gas particles move. As the particles cool and slow down, they condense into liquids. Liquid particles can have attractive forces including hydrogen bonding, dipole-dipole forces, etc. The same forces are even stronger in solids. The attractive forces affect the motion of the particles.

Background Info #2 – optionalPhases of Matter Phases of matter include: solid, liquid, gas, plasma, and Bose-Einstein condensates. Plasmas are much like gases but they are composed of electrically charged particles like ions and electrons. They’re the most common phase of matter in the visible universe. Plasmas are found in stars, solar wind, the ionosphere, auroras, and lightening. Plasmas are used in arc-welders and fluorescent tubes. The flame that you would see in a fire is a plasma. Bose-Einstein condensates are atoms at such low temperatures that they slow down and lose their individual identity. They form a cloud that behaves like a single object. Phases are determined by temperature and pressure.

Stop and Think Pg 87