The Foundations of Chemistry 1

Transcription

1 Te Foundations of Cemistry (a) Biocemistry is te study of te cemistry of living tings. (b) Analytical cemistry studies te quantitative and qualitative composition analysis of substances. (c) Geocemistry is te study of te properties and reactions of te substances tat compose eart s crust. (d) Nuclear cemistry is te study of te properties and reactions of atomic nuclei. (e) Inorganic cemistry is te study of compounds of elements oter tan carbon; owever, simple carbon compounds are also included, suc as CO, CO 2, carbonates, and bicarbonates. 1-3 (a) Matter is anyting tat as mass and occupies space. An eample of matter is your tetbook. (b) Kinetic energy is te energy of a moving object or te energy of an object due to its motion. A bowling ball as kinetic energy as it is rolling down te lane. (c) Mass is a measure of te amount of matter in an object. Te mass of a penny (a copper coin) is about 1 gram. (d) An eotermic process is a process tat releases eat energy. Te combustion of gasoline is an eotermic process tat is used in automobile engines. (e) An intensive property is a property tat is independent of te amount of material present. Density is an intensive property. 1-5 Law of Conservation of Matter and Energy: Te combined amount of matter and energy available in te universe is fied. Tis law recognizes tat te energy released in a nuclear reaction comes from te conversion of matter into energy. Te Law of Conservation of Matter and Law of Conservation of Energy refer to cemical (not nuclear) reactions and pysical canges. In cemical reactions and pysical canges, te quantity of mater as no detectable cange and energy is neiter created nor destroyed; energy is only converted from one form to anoter. 1-7 (a) Law of Conservation of Matter: Tere is no detectable cange in te quantity of matter during an ordinary cemical reaction or during a pysical cange. Eamples (i) wen magnesium metal burns in oygen, te mass of te product (magnesium oide) is equal to te sum of te masses of te magnesium and oygen tat combine; (ii) wen ice melts, its mass does not cange. (b) Law of Conservation of Energy: Energy cannot be created or destroyed in a cemical reaction or in a pysical cange; it can only be converted from one form to anoter. Eample in a ydroelectric plant, te mecanical (kinetic) energy of te falling water is converted into electrical energy; some of te energy is converted into eat. (c) Law of Conservation of Matter and Energy: Te combined amount of matter and energy available in te universe is fied. Eample te energy released in a nuclear reaction comes from te conversion of matter into energy. 1-9 An incandescent ligt bulb converts electrical energy into ligt energy. A considerable portion of te electrical energy used is converted into eat energy. Te Law of Conservation of Energy is observed since te sum of te eat energy and ligt energy produced is equal to te electrical energy consumed A omogeneous miture as uniform composition and properties trougout. Among te eamples given in tis eercise, carbon dioide (f) is te only pure substance. All samples of carbon dioide

2 would always contain te same ratio of carbon and oygen. Eamples (a), and (e) are omogeneous mitures; eamples (b), (c), (d), and (g) are eterogeneous mitures. Tey ave large particles tat are suspended (mud, onion), floating (ice), or tat are at te bottom of te container (cocolate cips); terefore, tey are not omogeneous mitures (a) A gaseous element is sown in bo (i). Te substance contains only one element because only blue speres are sown, even toug te element is diatomic. Te substance is a gas because te particles ave te maimum separation. (b) A gaseous compound is sown in bo (v). Te substance is a compound because eac particle contains two elements (two blue atoms and one red atom bonded togeter). Te substance is a gas because te particles ave te maimum separation. (c) A omogeneous gaseous miture is sown in bo (iv). A miture is sown because tere are two different types of particles (diatomic blue and a compound made of two blue and one red atom). Te substance is a gas because te particles ave te maimum separation. (d) A liquid solution is sown in bo (vi). A solution is a omogeneous liquid miture. A miture is sown because tere are two different types of particles (a compound made of one red and two wite atoms, wit a second compound made of one red, one blue, and four wite atoms). Te substance is a liquid because te particles are muc closer tan in a gas, but te particles are not as close as a solid or in a regular repeating pattern as a solid. (e) A solid is sown in bo (ii). A solid is sown because te particles are sown very close togeter and are in a regular repeating pattern. A crystalline solid is depicted. (f) A pure liquid is sown in bo (iii). Te substance is a liquid because te particles are all te same (maroon), are muc closer tan in a gas, but te particles are not as close as a solid or in a regular repeating pattern as a solid. Te liquid appens to be diatomic. Te liquid is pure because tere is only one type of particle (a) Te resulting combination would be a eterogeneous miture. Sand, candle wa, and sugar do not dissolve in eac oter. Te particles are unevenly mied due to size and density, producing a eterogeneous miture. (b) One could rinse te miture wit gasoline or anoter ydrocarbon, suc as ligter fluid, to dissolve te wa leaving te sand and sugar. Rinsing wit water would ten dissolve te sugar. Evaporation of te gasoline or ligter fluid used to rinse te miture would yield pure wa. Evaporation of te water rinse would yield pure sugar (a) Cemical properties are eibited as matter undergoes canges in composition, wereas pysical properties can be observed in te absence of any suc cange in composition. Eamples of cemical properties (i) magnesium can combine wit oygen; (ii) gasoline is flammable. Eamples of pysical properties (i) water is a colorless liquid at room temperature; (ii) oygen is a gas at room temperature and ordinary pressures; (iii) te melting point of bromine is 7.1 C. (b) Intensive properties are tose properties tat are independent of te amount of material eamined, wile etensive properties depend on te amount of material eamined. Eamples of intensive properties (i) magnesium can combine wit oygen; (ii) te melting point of bromine is 7.1 C. Eamples of etensive properties (i) te mass of a sample; (ii) te volume of a sample at specified conditions. 2

3 (c) Cemical canges occur wen one or more substances react resulting in te formation of one or more new substances. Pysical canges most often involve canges in pysical state brougt about by te absorption or release of energy Eample of cemical cange (i) alcool reacting (burning) in oygen to form carbon dioide and water. Eamples of pysical cange (i) ice melting to water wit te absorption of eat; (ii) steam condensing to liquid water wit te release of eat. (d) Mass is a measure of te amount of matter in an object, wile weigt is a measure of gravitational attraction of te eart for an object. An object aving a mass of 454 g as a weigt of one pound on Eart and te same object aving a mass of 454 g would ave zero weigt in a zero gravitational field (a) Cemical process. Iron is combining wit oygen in te presence of water to form a new substance (rust). (b) Pysical process. Water as a solid (ice) is canging to liquid water. Melting does not cange te composition. (c) Cemical process. Te wood is canged by te combustion or burning into as, wic is a new substance wit none of te properties of te wood. (d) Cemical process. Te components of te potato are broken down into substances tat can be absorbed by te digestive tract. (e) Pysical process. Dissolving sugar in water does not cange te composition. If te water in te solution were allowed to evaporate, te sugar would be left beind (a) Potential energy (b) Potential energy (c) Potential energy (d) Kinetic energy (e) Kinetic energy (f) Potential energy 1-23 (a) Eotermic. Te gasoline gives off eat during combustion or burning. (b) Eotermic. Te ice cream is canging from a liquid to a solid. Heat must be lost for te particles to slow down and to freeze. Tis is te opposite of melting. (c) Endotermic. Te cocolate absorbs eat as it melts or canges from a solid to a liquid. (d) Eotermic. As te temperature of te water drops, te eat energy is leaving te water and moving into te surroundings. (e) Eotermic. Water vapor gives off eat as it condenses. Te particles must cool to cange from a gas to a liquid (f) Eotermic. Te matc gives off eat as it burns. Tis eat can be used to ligt te wick of a candle Only pysical canges ave taken place. Te sulfur canged forms as it melted, ten cooled to form a different solid form but it was pure sulfur at eac step (a) (b) (c) (d) (e) (f) (a) Eact (te result of counting) (b) Eact (te result of counting) (c) Eact (counted to te nearest penny) (d) Not eact (obtained by measurement) (e) Not eact (obtained by measurement) (f) Eact (It migt be difficult to count 5,446 ants, but tat number of ants is still an eact number.) 3

4 1-31 Circumference = πd = ( )(7.46 cm) = 23.4 cm 1-33 (a) 10 6 (b) 10-3 (c) 10-2 (d) 10-1 (e) 10 3 (f) m, 53.8 mm, km, and micrometers 1-37? cm = in 2.54 cm 1 in = 26.0 cm? cm = 7.75 in 2.54 cm 1 in = 19.7 cm 26.0 cm 19.7 cm 1-39? $ = 14 gal 4 qt 1 gal 1 L qt $ L = $ 31.55, wic rounds to $ ? g = 8.92 g cm cm 11.4 cm 8.9 cm = g 1-43? g = 3.00 L 1000 cm3 1 L g 1 cm 3 = g (if tree L as 3 sig. figs.) 1-45 (a) mass of water = g g = g water volume of water = g 1 cm g = cm3 (b) mass of unknown liquid = g g = 9.51 g density of unknown liquid = M V = 9.51 g cm3 = g/cm3 1-47? g = ml g soln. ml 40.0 g acetic acid 100 g soln. = g acetic acid 1-49 (a)? K = 275 C = 548 K (b)? C = K = C (c)? F = 47.0 C 1.8 F + 32 F = 52.6 F 1.0 C (d) First convert F to C, ten C to K.? C = 1.0 C 1.8 F (100.0 F 32 F) = 37.8 C wit only 2 sig figs? K = (37.8 C ) = 311K 1-51 (a)? F = 37 C 1.8 F + 32 F = 99 F 1.0 C (b)? F = 37 C 1.8 F + 32 F = 35 F 1.0 C 4

5 (c)? C = 1.0 C 1.8 F (110 F 32 F) = 43 C 1-53 He:? C = 4.2 K C = C? F = 1.8 F ( C) + 32 F = F 1.0 C N 2 :? C = 77.4 K C = C? F = 1.8 F 1.0 C ( C) + 32 F = F 1-55 Tis eercise sould read mp = C, not mp = C. A negative C is lower tan absolute zero and, terefore, is not a logical value.? F = 1.8 F 1.0 C C + 32 F = F 1-57 Temperature cange = 32.0 C 15.0 C = 17.0 C? J = mass of substance specific eat temperature cange = 78.2 g J g C 17.0 C = J 1-59? J = mass of substance specific eat temperature cange = 19.5 g 4.184J g C (34.2 C 90.0 C) = J or J must be removed 1-61? g H 2 O = 236 ml g 1 ml = 235 g H 2O? J = 235 g 4.184J g C? kj/min = J 2.00min (78. C 25. C) = J 1 kj 1000 J = 26 kj/min 1-63 (a)? g calcium carbonate = g sample (b)? g sample = 18.8 g calcium carbonate g calcium carbonate = 100g sample 19.5 g calcium carbonate 100g sample 25.8g calcium carbonate = 72.9 g sample 1-65 Radius of eart s orbit (m) = km 103 m 1 km = m Radius of ydrogen atom (m) = 0.37 Å m 1 Å = m Ratio = m m =

6 1-67? km = 65 mi km mi km = = km/ 1-69 (a) (b) 1.00 mi 4.90 min 19.7 km (c) m 60 min km = 19.7 km/ mi 1 60 min 1 min 60 s 1000 m 100 cm 1 km 1 m = 547 cm/s km 1 km 60 min 1000 m s 1 min = 274 s 4 min 34s 1-71 If you wanted te pot or pan to eat up quickly, you would select material tat as a small specific eat value. If you wanted te pot or pan to retain its temperature once it is ot, ten you would select material tat would ave a iger specific eat. Most individuals desire some of bot of tese traits but feel tat te first is te more important Te density of newly-minted penny, g/cm 3 = (0.027)(8.72 g/cm 3 ) + ( )(7.14 g/cm 3 ) = 0.24 g/cm g/cm 3 = 7.18 g/cm We know tat water must be more dense, because ice floats in water Te correct answer is (a). Te particles would be te same size but closer togeter at te lower temperature (a) Let = te reading on te Celsius termometer = te reading on te Fareneit termometer F = C 1.8 F 1.0 C + 32 F or, witout units, = ; 0.8 = -32 ; = 40 C, = 40 F (b) 2 = ; 2 = ; 0.2 = 32; = 160 C, 2 = 320 F (c) = ; 2.8 = 32; = 11.4 C, - = F 1-81 Tere are many possible answers. One possible answer is: Wic of te following are mitures, wic are compounds, wic are elements? Dry air, etane (C 2 H 6 ), aluminum, salt water, calcium carbonate. Please formulate a different question as your answer Students know many cemical terms before tey begin to read tis tetbook. A few of te terms tat tey are likely to know are: compound, distillation, and cemical reaction (a) A gas is sown in boes (iii), (iv), (vii), and (i). Te particles are in te gas pase because te particles ave te maimum separation and are in a random arrangement. (b) A liquid is sown in boes (v -te blue particles in te top rigt of te diagram) and (viii). Tese are liquids because te particles are muc closer tan in a gas, but te particles are not as close as a solid or in a regular repeating pattern as a solid.

7 (c) A solid is sown in boes (i), (ii), (v- te brown particles in te bottom left of te diagram), and (vi). A solid is sown because te particles sown very close togeter and are in a regular repeating pattern. (d) An element is sown in boes (i), (iv), and (vi). Te particles are all te same color (blue), even toug te blue atoms in bo (vi) are sown as diatomic particles. (e) A compound is sown in bo (iii). Te compound depicted ere is composed of one blue atom and one brown atom, since one blue is attaced to one brown trougout. Te arrangement of te compound sows tat it appens to be in te gaseous state. (f) A miture is sown in boes (ii), (vii), and (i). Mitures contain two or more different types of particles. Boes (ii) and (vii) contain bot blue and brown particles. Bo (i) contains diatomic blue particles and single brown particles. Boes (v) and (viii) sow two types of particles, but tese particles are not yet mied. (g) A pure substance is sown in boes (i), (iii), (iv), and (vi). A pure substance contains particles tat are identical. 7