8th Grade 2nd 9 Weeks Benchmark Study Guide Observing Chemical Change Observable Changes
Type of Change Baking a Cake ­ 1. turns from gooey to fluffy, a smell is released 2. chemical Burning a Log ­ 3. turns from brown to black, a smell is released 4. chemical Freezing Water ­ 5. turns from liquid to solid
6. physical 7. Any change that alters a substance without changing it into another substance is a ​
physical change. 8. ​
Matter​
is anything that has mass and takes up space. 9. A reaction that releases energy in the form of heat is called an ​
exothermic reaction​
. 10. An ​
endothermic reaction​
is a reaction in which energy is absorbed. 11. A chemical change is also referred to as a ​
chemical reaction​
. 12. A ​
precipitate​
is a solid formed from a solution during a chemical reaction. 13. ​
Chemistry​
is the study of the properties of matter and how matter changes. Describing Chemical Reactions 1. FeS + HCl > FeCl​
+ H​
S
a. FeS + 2HCl > FeCl​
+ H​
S
b. replacement 2​
2​
2​
2​
2. Na + F​
> NaF
a. 2Na + F​
> 2NaF
b. synthesis 2​
2​
3. HgO > Hg + O​
a. 2HgO > 2Hg + O​
b. decomposition 2
2
4. Describe in words the chemical composition of the molecules involved and the reaction represented by the equation: 2H​
+ O​
> 2H​
O 2​
2​
2​
2 molecules of a compound containing 2 Hydrogen atoms and 1 molecule of a compound containing 2 Oxygen atoms combine to create 2 molecules of a compound containing 2 Hydrogen atoms and 1 Oxygen atom. 5. Use the principle of conservation of mass to explain why the equation in question 4 is balanced. There are 4 Hydrogen atoms on the left and 4 Hydrogen atoms on the right. There are 2 Oxygen atoms on the left and 2 Oxygen atoms on the right. Since there are equal numbers of atoms of each element on both sides of the equation, no matter was created or destroyed, thus supporting the law of conservation of mass. 6. chemical equation ­ C. uses symbols and formulas to show chemical reactions 7. decomposition reaction ­ G. reaction in which compounds are broken down into simpler products. 8. coefficient ­ F. number telling how many molecules of a substance are involved in a chemical reaction. 9. product ­ A. substance present after a reaction 10. reactant ­ E. substance present before a reaction 11. conservation of mass ­ H. principle that states that matter is not created or destroyed during a chemical reaction 12. synthesis reaction ­ B. reaction in which substances combine to form a more complex compound 13. replacement reaction ­ D. reaction in which one element replaces another in a compound Handwritten Page 1. Define solution: a mixture containing one or more solute(s) dissolved in a solvent with particles so small that they cannot be seen, does not scatter light, substances are uniformly distributed Define colloid: a mixture containing two or more different substances with particles so small that they are very difficult to see (larger than solution particles), do scatter light, ​
Define suspension: a mixture containing two or more different substances with large particles that are easily seen, substances are unevenly distributed 2. Examples of a solution: salt water, sugar water, air, gasoline, brass Examples of a colloid: jello, milk, mayonnaise, fog Examples of a suspension: Italian salad dressing, salad, granite, cereal with milk 3. Differentiate between solute and solvent. A solute is the substance in a solution that dissolves while a solvent is the substance in a solution that does the dissolving. A solute is found in a smaller proportion than a solvent. 4. Differentiate between elements, ionic compounds, molecular compounds, and mixtures. Elements are the smallest forms of matter that have unique characteristics and cannot be broken down further into smaller substances. Compounds form when 2 or more elements chemically combine, forming chemical bonds. Ionic compounds are formed by the creation of ionic bonds (giving and receiving valence electrons). Molecular (covalent compounds) are formed by the creation of covalent bonds (sharing of electrons. Ionic compounds conduct electricity when dissolved in water (because they separate into individual ions) while molecular compounds do not conduct electricity when dissolved in water (because they are not made up of ions). Compounds can only be separated by chemical means. Mixtures form when 2 or more substances are physically combined. They can be separated by physical means such as evaporation (different substances evaporate at different temperatures), freezing (different substances have different freezing points), filtration, and picking parts out by hand. 5. Calculate density Formula = Mass/Volume Unit = grams/milliliters 6. Define mass: The amount of matter in an object/substance. Define volume: The amount of space an object/substance takes up. Define density: The amount of matter in a given amount of volume of a substance. Define matter: Anything that has mass and takes up space. 7. Determine ion charges based on numbers of valence electrons. lose 2 electrons = +2 lose 1 electron = +1 gain 2 electrons = ­2
gain 1 electron = ­1 8. Define malleable: A metal’s ability to be hammered into thin sheets and shaped into different shapes. Define ductile: A metal’s ability to be drawn out into thin wires. 9. Differentiate between an open system and a closed system. An open system is one where matter outside of a reaction may enter and where matter within the reaction may exit. A closed system is one where matter outside of a reaction cannot enter and where matter within the reaction cannot exit. 10. Read a periodic table. Atomic # = # of protons Atomic mass = # of protons + # of neutrons 11. Determine # of protons from # of electrons. # of electrons = # of protons Determine # of neutrons from # of protons. Atomic mass ­ # of protons = # of neutrons Determine # of protons from # of neutrons. Atomic mass ­ # of neutrons = # of protons