Determine if each statement describes an exothermic process (EXO) or endothermic process (ENDO). _EXO_ H is negative

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1 South Pasadena Chemistry Name Period Date S T A T I O N 1 E N D O / E X O Determine if each statement describes an exothermic process () or endothermic process (). H is negative surroundings get warmer energy diagram is uphill combustion of propanol H is positive reactants have more energy than products CaCO 3(s) + heat CaO(s) + CO 2(g) q < 0 q > 0 inter-particle attractions strengthen surroundings get colder H 2(g) + ½O 2 (g) H 2O (l) + heat products have more energy than reactants condensation of water H 2O (l) H 2O (g) water, when placed in the freezer S T A T I O N 2 M O R E E N D O / E X O Determine whether each process is an Endothermic () or Exothermic () process. The baggie gets hotter when CaCl 2 (s) is dissolved. A hot aluminum slab cools down in a beaker of water. Ethanol undergoes combustion. Ethanol vapor condenses to liquid. The baggie gets colder when NH 4Cl (s) is dissolved. A beaker of water is warmed when a hot aluminum slab is placed in it. Water freezes into ice when placed in a freezer. The size of a balloon shrinks when placed over ice. Ethanol liquid vaporizes when heated by a person s hands. A block of ice melts in the sun.

2 S T A T I O N 3 S P E C I F I C H E A T L A B An experiment was carried out to determine the specific heat of a slab of an unknown metal. Record the data. A 175-mL sample of water was placed in a Styrofoam cup, and the temperature of 25.5 C was recorded. The metal slap was carefully taken out of a beaker of boiling water at C and submerged into the water in the Styrofoam cup. The temperature of the water with the metal slab rose to 28.7 C. The mass of the dry metal slab was found to be 86.8 g. Volume of Water 175 ml Mass of Metal 86.8 g Initial Temp of Water 25.5 C Initial Temp of Metal C Final Temp of Water 28.7 C Final Temp of Metal 28.7 C Calculate the energy absorbed by the water. (C p of water = 4.18 J/g C.) Water s density is 1.00 g/ml. q = m C p T = (175 ml) 1 g (4.18 J/g C) (28.7 C 25.5 C) = 2341 J 1 ml Calculate the specific heat of the metal. q = m C p T ( 2341 J) = (86.8 g) (C p) (28.7 C C) C p = J/g C Determine the identity of the unknown metal and calculate % error of the experiment Zn % Error = 100% = 2.3% Metal Cp (J/g C) Al Fe Mg 1.02 Zn S T A T I O N 4 S P E C I F I C H E A T Answer each question and explain briefly. 1. Silver and sodium have specific heats J/g C and 1.20 J/g C, respectively. (a) 40 gram blocks of each metal at 20 C are placed in a hot stove for the same amount of time. Which metal will have a higher temperature when they are taken out? Silver has lower specific heat, is easier to change temp, so will change temp more than sodium resulting in higher final temperature. (b) Samples of each block are heated by adding 3000 J of energy. The temperatures of both blocks increase by 120 C. Which metal has a larger mass? Silver is easier to change temp, so with the same energy and same change in temp, silver can heat up a larger amount/mass. (c) 20 gram samples of each metal at 15 C are heated until they reach 50 C. Which metal required more energy? Sodium has higher specific heat, so is harder to change temp and will require more energy. 2. Warm samples of liquids X and Y each has a mass of 80 g and are at 25 C. When the samples are cooled so that 200 cal are released, liquid X has a final temperature of 15 C, and liquid Y has a final temperature of 5 C. Which has a greater specific heat? Liquid X changed a smaller amount of temp, so it s harder to change its temperature, having a greater specific heat.

3 S T A T I O N 5 C H A N G E S I N T E M P E R A T U R E Show all work. (Identify variables, write equation, substitute values, write answer.) 1. How much energy is required to increase the temperature of a 25.0 g sample of steam from 150 C to 180 C? (C p = cal/g C) q =? m = 25.0 g q = m C p T = (25.0 g)(0.497 cal/g C) (30 C) = 373 cal C p = cal/g C T = 180 C 150 C = 30 C 2. What is the initial temperature of an 8.5 gram piece of gold if, after applying 220 J of heat, the temperature rose to 350 C? (C p = J/g C) q = 220 J m = 8.5 g q = m C p T T = 350 C T i (220 J) = (8.5 g) (0.129 J/g C) (350 C T i) C p = J/g C T i = 149 C S T A T I O N 6 C A L O R I M E T R Y A 100. g aluminum block (C p = J/g ºC) in boiling water is added to an insulated cup containing 50.0 grams of water (C p = J/g ºC) at 5.00ºC. Calculate the final temperature of the mixture. Aluminum m = 100. g C p = J/g C T = x 100 C Water m = 50.0 g C p = J/g C T = x 5.00 C q Al = +q H2O (m Al)(C Al)( T Al) = +(m H2O)(C H2O)( T H2O) (100 g)(0.900 J/g C)(x 100 C) = +(50.0 g)(4.184 J/g C)(x 5.00 C) x = 33.6 C

4 S T A T I O N 7 H E A T S O F F U S I O N & V A P O R I Z A T I O N Answer each question and explain briefly gram pieces of solid gold and silver were placed in separate hot ovens at their respective melting points. When they were taken out, all of the gold had melted, while only half of the silver half melted. Which metal has a higher value for H fus? Silver melted less, so it s harder to melt silver than gold, and it has a higher H fus cal of heat was applied to samples of water and ethanol at their respective boiling points. At exactly five minutes, both samples were completely vaporized. Which sample had the greater mass? ( H vap for water = 540 cal/g, ethanol = 200 cal/g) Since ethanol has a lower Hvap, it s easier to vaporize ethanol than water, so with the same energy, more mass of ethanol was vaporized. 3. Which liquid water or ethanol has stronger inter-particle attractions? ( H vap for water = 9.7 kcal/mol, ethanol = 9.2 kcal/mol) Since water has a higher H vap, it takes more energy to break the inter-particle attractions so its attractions are stronger. S T A T I O N 8 C H A N G E S I N S T A T E S Show all work. (Identify variables, write equation, substitute values, write answer.) 1. What is the value of q when 31.6 grams of water freezes at 0 C? ( H fus = 333 J/g) q =? q = m H fus = (31.6 g)(333 J/g) = J m = 31.6 g H fus = 333 J/g 2. How many grams of CO 2 can be vaporized when 500 cal is applied at its boiling point, 57 C? ( H vap = 83.2 cal/g) q = 500 cal q = m H vap m =? (500 cal) = m (83.2 cal/g) H vap = 83.2 cal/g m = 6.01 g 3. What is the value of H vap of ammonia in J/g if 18,500 J of heat is required to vaporize a 13.5 g sample? q = 18,500 J q = m H vap m = 13.5 g (18,500 J) = (13.5 g) H vap H vap =? H vap = 1370 J/g

5 Sketch the heating curve for water from 30 C to 140 C. Label the axes (with units), and the Freezing and Boiling points. Label the 140 C segments (a) - (e). Identify the state(s) of matter of each segment. In which segment(s): (circle) are inter-particle attractions weakening? a b c d BP=100 C e is the temperature increasing? a b c d e are the processes endothermic? a b c d e FP=0 C are the processes exothermic? a b c d e do you use q = m C p T? a b c d e 30 C do you use q = m H? a b c d e S T A T I O N 9 H E A T I N G C U R V E A 50.0 gram sample of ice at 0.0 ºC is heated until it is liquid at 80.0 ºC. Indicate on the heating curve where the heating process begins and ends. Calculate the energy absorbed by this process. For water, H fus = 333 J/g, H vap = 2260 J/g, C ice = 2.10 J/g C, C water = 4.18 J/g C, C steam = 2.08 J/g C q b = (50.0 g) 333 J = J g q c = (50.0 g)(4.184 J/g C)(80 C 0 C) = J q = q b + qc = 16,700 J + 16,700 J = 33,400 J (b) solid/liq (a) uid solid (c) liquid (d) liquid/g as (g) gas