Kinetic Molecular Theory, Gases, and Phase Changes (Answer Key) solid liquid melting sublimation freezing evaporation condensation deposition gas 8. See above. 9. Endothermic: melting, evaporation, sublimation. Exothermic: freezing, condensation, deposition. Melting is endothermic because energy is absorbed by the solid in order to break intermolecular forces (IMFs) and become a liquid. Freezing is exothermic because the particles of the liquid lose kinetic energy, slow down, and form intermolecular forces to become a solid. 10. A to B: Solid is heating up (increasing temperature) as energy is added B to C: Solid intermolecular forces (IMFs) are breaking as energy is added, temperature is NOT increasing. C to D: Liquid is heating up (increasing temperature) as energy is added D to E: Liquid IMFs are breaking as energy is added, temperature is NOT increasing. E to F: Gas is heating up (increasing temperature) as energy is added 11. Adding energy causes the kinetic energy of particles to increase, increasing temperature and breaking intermolecular forces and causing a phase change. Removing energy allows particles to slow and form new intermolecular forces, also causing phase changes. 12. Intermolecular forces are the forces of attraction between particles holding them together. Solids have strong IMFs, liquids have medium IMFs, and gases have weak or no IMFs at all. 13. Conduction is the transfer of heat through a material. When heat is applied to one location, the particles there gain kinetic energy and move more rapidly. They collide with their neighbors, giving them increased kinetic energy, and those neighbors collide with their neighbors, and so on throughout the material. Conduction happens much more quickly in solids because the particles are always side by side and collide much more often and easily. In a gas, particles are so far apart that they almost never collide, so the added kinetic energy is not transferred. 14. A solid consists of particles in a rigid arrangement, permanently held next to their neighbors by intermolecular forces. These particles are constantly vibrating in place. A liquid consists of particles still close together, but able to flow past and around each other. A gas consists of particles far apart from each other, moving freely and rarely colliding.
15. a) As temperature of a gas increases, pressure increases. (direct relationship) (Gay Lussac Law) *Volume is constant b) As temperature of a gas increases, volume increases. (direct relationship) (Charles Law) *Pressure is constant c) As the volume of a gas increases, the pressure decreases. (inverse relationship) (Boyle s Law) *Temperature is constant Graphs: 16. Increasing kinetic energy causes temperature to increase, which also causes volume and pressure to increase. 17. The particles of the ice cube have low kinetic energy and are held together by strong IMFs because they are in the solid state. The particles of the soda are warmer and moving around with greater kinetic energy because they are in the liquid state. The particles of the soda collide with the particles of the ice cube. This causes some of the intermolecular forces to break and the ice cube particles gain kinetic energy, eventually breaking free from the ice cube and becoming liquid. The soda particles lose energy in the collisions, so the drink gets colder. Acid, Base Chemistry (answer key) Strong acid Weak acid Neutral Weak base Strong base 18. See above. 19. Limestone (calcium carbonate) is a weak base that keeps lake water at a ph of 8-9. When acid rain falls in these lakes, the base neutralizes the acid rain, maintaining a ph near 7, so the lake does not get too acidic. Lakes with granite rocks do not have the protective base properties, so the acid rain causes the ph of the lake water to fall, harming animals and plants. 20. Red litmus paper turns blue in a base; blue litmus paper turns red in an acid. 21. Hydronium is H 3O +. It is formed when an acid releases H + which combines with H 2O
22. At a ph of 0, hydronium/hydrogen ion (H 3O + ) concentration is very high and the solution is very acidic, and there is zero hydroxide (OH - ). At a ph of 14, the concentration of OH - is very high, while the concentration of H 3O + is zero. At a neutral ph of 7, the concentration of OH - and H 3O + is exactly equal. 23. Arrhenius acid: produces H +. Arrhenius base: produces OH -. Brønsted-Lowry acid: donates H +. Brønsted-Lowry base: accepts H + 24. Generally, a compound starting with H is an acid. Compounds containing OH are bases. NH 3 (ammonia) is another common base. HCl acid (hydrochloric acid) NaOH base (sodium hydroxide) KOH base (potassium hydroxide) HBr acid (hydrobromic acid) NH 3 base (ammonia) (accepts proton to become NH 4 +) HNO 3 acid (nitric acid) Mg(OH) 2 base (magnesium hydroxide) HF acid (hydrofluoric acid) H 2SO 4 acid (sulfuric acid) 25. A neutralization reaction always produces WATER and SALT (ionic compound). The general equation is: Acid + base à water + salt 26. a) 2KOH + H 2CO 3 2H 2O + K 2CO 3 (NOTE: CO 3 2- has a 2- charge, while K + has a 1+ charge, so two K + ions are needed to balance) b) HF + LiOH H 2O + LiF Organic Chemistry (Answer key) 27. An organic compound contains carbon. (Specifically, carbon bonded to hydrogen) 28. Carbon can form 4 bonds because it has 4 valence electrons, so it has 4 empty slots to form bonds. 29. Ethane C 2H 6 Pentane C 5H 12 Propane: C 3H 8
NAMING TIP: Hydrocarbons (chains of hydrogen and carbon) are named by their number of carbons starting at 5. PENTANE = 5, HEXANE = 6, HEPTANE = 7, OCTANE = 8. 30. C 6H 14 is hexane its structural isomers include any arrangement of carbons in single bonded chains, straight or branched. There are five possibilities. It is helpful to draw them simply as lines, where each corner is a carbon. Two different ways of drawing them are shown below.