Thermochemistry-practice-problems PDF

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T hermo chem ist ry pr act ice pro b lems

1) Ho w A) B) C) D)

can ene rgy be transfe rr ed to or from a system? En e rgy can only be transfe rr ed as po tential ene rgy be ing conv erted to kin etic ene rgy . En e rgy can be transfe rred only as heat. En e rgy can be transfe rr ed onl y as work . En e rgy can be transfe rr ed a s heat a nd/or w ork .

1)

2) Which of the following is an exa m pl e of a state fun ct ion ? A) Th e le ng th of t im e it takes to go from N e w York to Lo s Ang eles B) Th e mil eage traveled going from San Fr ancisco to Los A ngeles C) Th e a moun t of t im e it takes to cha ng e the cha nn el w h e n Gossip Girl comes on . D) Th e diff erence in altit ud e bet ween C hica go a nd De nv e r

2)

3) Which of the following is N O T a state prop erty? A) pr essur e B) temperature C) in te rn al ene rgy D) enthalpy E) work

3)

4) Which of the following is the best exa mpl e of an isol ated system? A) water in a st yrofo am coff ee c up B) liquid in a beaker wi th a watch gl ass ov er it C) sod a in an unop ened sof t drink ca n D) coffee in a c losed t hermos bottle

4)

5) H ow A) B) C) D)

5)

does a close d system diff er from an op en system? A closed system does not do a ny w ork on t he surroundings. A closed system ca nno t exchange he at w ith t he surroundings. En e rgy is con se rv ed in a c losed system, bu t no t in an op en system. A closed system ca nno t exchange matter w ith t he surroundings.

6) A chemical r eaction whe r e h eat is transferred to t h e surroun dings is a(n) ___________________ reaction.

7) Which of the following is an e ndo the rmi c process? A) j et fuel burning in a j et engine C) fr ee zing of w ate r

7) B) combustion of methane D) vapori z at ion of water

8) Whi ch is t ru e if ∆ H = - 95 J? A) Bo th the system a nd the s urroundings are ga ining 95 J. B) Bo th the system a nd the surrounding s are lo sing 95 J. C) Th e system is ga ining 95 J, while t he surroundings a re lo sing 95 J. D) Th e system is losing 95 J, while t he surroundings a re gaining 95 J. E) T h e system is losing - 95 J, while t he surroundings a re gaining 95 J.

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8)

9) Whi ch of the following sign s on q a nd w re p r esent a system t hat is doing work on t he surroundings, as well as losing heat t o t he surroundings? A) +q , + w B) - q , - w C) +q , - w D) - q , + w E) N on e of the a bov e.

9)

10) Ho w mu ch w ork in j oul es is don e wh en a p ist on e xp a nd s from a volum e of 13.27 li ters t o 76.55 liters a gainst a pr essur e of 14.89 at m?

10)

11) H ow m u ch work in j oul es is don e on t he system w h en a 1.15 atm exte rn al p ress ur e causes a piston to decrease in volume from 6.55 liters t o 3.16 liters?

11)

12) In a re frig erat ion system, t he re frig erant gas absorb s 21.39 kJ of energy while expanding against a 0.278 at mosph ere pr essur e f rom a volu me of 0.0423 liters t o a volume of 1.876 li ters. Wh at is th e e n e rgy cha ng e of the gas?

12)

13) W h at is t he ene rgy cha ng e of the system if a che mi cal react ion transfers 32.146 kJ of heat to the surroundings w hile it ca uses t he expansion of a 1.465 liter vessel t o 3.687 liters a gainst a pr essur e of 3.64 atmosph eres?

13)

14) Lead, water, sulfur , a nd arse nic have specifi c heats of 0.128, 4.18, 0.706, a nd 0.329J/g° C, r espect iv e ly . W hi ch of these would r equire the sma ll est a moun t of heat to increase its temperat ure by 10 °C (assume a ll samples have t he same mass)?

14)

15) Wh en pow er w as t urn ed off to a 30.0 gal. w ater heater , t he t em perature of t he wat er dropp ed f rom 75.0 °C to 22.5 °C. H o w mu ch heat w as lost to t he s urrounding s? (1 gal = 3.785 L)

15)

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16) Ho w mu ch heat is needed to raise t he te mp erat ur e of 5.28 gal of water from 25.0 °C t o 88.0 °C (1 gal = 3.785 L)?

16)

17) 14.0 g of met al at 24.0 °C has 250 joules of he at a dded t o i t. T he metal's specific heat i s 0.105 J/g °C. W h at is its fin al te m p erat ur e?

17)

18) 1219 joules of heat raise t he t emp erat ure of 250 g of metal by 64 °C . W h at is t he specifi c heat in J /g °C?

18)

19) 1674 J of heat a re absorbed by 25.0 m L of a n a qu eou s solution of N a O H (d = 1.10 g/mL , specific heat = 4.10 J/g °C). Th e te mp erat ur e of the solu t ion goes up how ma ny de grees?

19)

20) W h at is t he fin al te m p erat ur e wh en 150.0 m L of w ater at 90.0 °C is a dd ed to 100.0 m L of w ater at 30.0 °C?

20)

21) 50.0 g of iron t h at has a n initial temperat ure of 225 °C a n d 50.0 g of gold t h at has a n initial temperature of 25.0 °C a re brough t into con t act w ith one a nother . Assuming no heat is lost to t he surrou ndings, wh at w ill be t he tem perature w hen t he t w o metals reach t hermal equilibriu m ? T h e sp ecif ic heat ca pacity of iron = 0.449J/g°C a n d gold = 0.128 J/g°C.

21)

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22) 100.0 g of nickel at 150 °C w as p laced in 1.00 L of water at 25.0 °C . The final t emp erat ure of the water was 26.3 °C. W h at is t he specifi c he at of nickel?

22)

23) A 25.0 g piece of iron at 398 K is placed in a st yrofo am coff ee c u p con ta ining 25.0 mL of water at 298 K. Assuming that no h eat is lost to the cu p or t h e surroundings, wh at w ill t he fin al te mp erat ur e of t he w ater be? T h e spec ifi c heat capacity of iron = 0.449J/g°C a n d w ater = 4.18 J/g° C.

23)

24) W h at is t he mol ar mass of a metal p r e di cted by the D ulong - Petit la w if t he metal has a specific heat capacity of 0.128J/g°C?

24)

25) A 75.0 g samp l e of a metal at is heated by a d ding 450 J of heat. Its t emp erature increased from 22.0 °C to 37.0 °C. W h at is the mol ar mass of the metal?

25)

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26) A 10.0 g sampl e of a metal at 78.0 °C is subm e rg ed in 50.0 mL of w ater at 25.0 °C. the f in a l temperature of t he w ater is measured t o be 26.1 °C . Assuming no heat is lost t o t he surroundings, w h at i s t he a pproximate molar mass of the metal?

26)

27) T wo aqu e ou s solu t ion s at room te m p erat u r e are mix ed in a coff ee cu p ca lorim eter. T h e react ion ca uses t he t emper at ure of t he resulting solution t o fall below room temper at ure. Which of t he follow ing statements is T RU E? A) En e rgy is lea ving the system during react ion. B) Th e produ cts have a low er po tential ene rgy than the reactants. C) T hi s t yp e of e xp e rim ent dir ect ly yi e ld s ∆E rxn . D) Th e mixing is e ndo the rmi c. E) Th e solu t ion has special p rop erties t hat ena bl e it to viol ate t he fir st a n d second law of thermod ynamics. 28) A 21.8 g sample of ethanol (C 2 H 5 O H ) is burned in a bomb calorim eter. If t he te m p erat ur e ri ses from 25.0 °C to 62.3 °C, dete rmin e the heat capacity of t he calorim eter. T h e mol ar mass of ethanol is 46.07 g/mol. C 2 H 5 O H(l) + 3 O 2 (g)  2 C O 2 (g) + 3 H 2 O(g)

∆ H rxn = - 1235 kJ

29) A 35.6 g sample of ethanol (C 2 H 5 O H ) is burned in a bomb ca lorim eter that has a heat ca p ac it y of 23.3 kJ/°C. If the t e mp erat ur e rose from 35.0 °C to 76.0 °C, wh at is the value of ∆ H rxn ? T h e mol ar mass of etha nol is 46.07 g/mol . C 2 H 5 O H(l) + 3 O 2 (g)  2 C O 2 (g) + 3 H 2 O(g)

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28)

∆ H rxn = ?

29)

27)

30) A 12.8 g sample of ethanol (C 2 H 5 O H ) is burned in a bomb ca lorim eter that has a heat ca p acity of 5.65 kJ/°C. If t he ini tial te mp erat ur e is 25.0 °C , determine t he final t emperature of t he calorim eter. T h e mol ar mass of etha nol is 46.07 g/mol . C 2 H 5 O H(l) + 3 O 2 (g)  2 C O 2 (g) + 3 H 2 O(g)

30)

∆H rxn = -1235 kJ

31) A 100.0 mL sampl e of 0.300 M N aO H is mixed w ith a 100.0 mL sample of 0.305 M H N O 3 in a coff ee c up calorim eter. If both solu t ion s w ere ini tia lly at 35.0 °C a nd t he t emperature of the res ul t ing solu t ion w as record ed as 37.0 °C, dete rmin e t he ∆ H rxn (in uni ts of kJ/mol).

31)

Assum e that no h eat is lost to t h e calorim eter or t h e surroundings.

32) A student is pr epa ring to perform a se ri es of calorim et ry exp erim ents. She first w i shes t o determine t he heat capacity of the ca lorim eter (C cal ) for h er coff ee cu p ca lorim ete r . S h e

32)

pours a 50.0 mL sample of w ater at 72.0 °C into t he ca lorimeter c ontaining a 50.0 mL sample of water at 25.0 °C . She car ef ull y r ecords t he final t emperature of t he water as 44.0 °C. What is t he v alue of C cal for the ca lorim eter?

33) T wo solu t ion s, ini tia lly at 24.60 °C , a re mixed in a coffee c up calorimeter (C cal = 15.5J/°C). W h en a 100.0 mL volu m e of 0.100 M A g N O3 solu t ion is mix ed w i th a 100.0 mL sample of 0.200 M N aCl solution , t he t emperature in t he calorimeter rises t o 25.30 °C . Determine t he ∆ H rxn for the react ion as w ri tten be low . N aCl (aq) + A gN O3 (aq)  A gCl(s) + N a N O 3 (aq)

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∆ H rxn = ?

33)

34) Use the ∆ H ° f inform at ion provid ed to calc ul ate ∆ H ° rxn for the following: ∆ H ° rxn = ?

SO 2 Cl 2 (g) + 2 H 2 O(l)  2 H Cl(g) + H 2 S O4(l)

SO 2 Cl 2 (g)

∆ H ° f (kJ/mol) - 364

H 2 O(l)

- 286

H C l(g) H 2 SO 4 (l)

- 92 - 814

35) Use t h e inform at ion provided to determine ∆ H ° rxn for t h e follow ing reaction: C H 4 (g) + 4 Cl 2 (g)  C Cl 4 (g) + 4 H Cl(g)

34)

35)

∆ H ° rxn = ?

∆ H °f (k J/mol) C H 4 (g) C Cl 4 (g)

- 75 - 96

H C l(g)

- 92

36) Use t h e inform at ion provided to determine ∆ H ° rxn for t h e follow ing reaction: 3 Fe2 O 3 (s) + C O(g)  2 Fe 3 O 4 (s) + C O 2 (g)

36)

∆ H ° rxn = ?

∆ H °f (kJ/mol) Fe2 O 3 (s)

- 824

Fe3 O 4 (s)

- 1118

C O(g) C O 2 (g)

- 111 - 394

37) Use the ∆ H ° f and ∆ H ° rxn inform at ion provid ed to calc ul ate ∆ H °f for IF: IF 7 (g) + I 2 (g)  IF 5 (g) + 2 IF(g)

IF 7 (g)

∆ H ° f (kJ /mol) - 941

IF 5 (g)

- 840

∆ H ° rxn = - 89 k J

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37)

38) Use t h e stan d ard react ion enthalpies gi ven below to determine ∆H ° rxn for t h e f ollo wing reaction: 2 N O(g) + O 2 (g)  2 N O 2 (g)

∆ H ° rxn = ?

N 2 (g) + O 2 (g)  2 N O(g)

∆ H ° rxn = 183 kJ

1/2 N 2 (g) + O 2 (g)  N O 2 (g)

∆ H ° rxn = 33 kJ

38)

Given:

39) Use t h e stan d ard react ion enthalpies gi ven below to determine ∆H ° rxn for t h e f ollo wing reaction: P4 (g) + 10 Cl 2 (g)  4 PCl 5 (s)

∆ H ° rxn = ?

PCl 5 (s)  PCl 3 (g) + C l 2 (g)

∆ H ° rxn = 157 kJ

P4 (g) + 6 C l2 (g)  4 P Cl 3 (g)

∆ H ° rxn = - 1207 kJ

39)

Given:

40) Ho w mu ch ene rgy is released during the form at ion of 98.7 g of Fe, according t o t he reaction below? Fe2 O 3 (s) + 2 A l(s)  A l 2 O 3 (s) + 2 Fe(s)

40)

∆ H ° rxn = - 852 kJ

41) Using the following inform at ion , wh at mass of H F m u st react in order to produ ce 345 kJ of energy ? A ssum e exc ess SiO 2 . SiO 2 (s) + 4 H F(g)  SiF 4 (g) + 2 H 2 O (l)

41)

∆ H ° rxn = - 184 kJ

42) Using the follow ing inform at ion , w h at mass of H 2 O mu st form in ord er to prod u ce 975 kJ of ene rgy? SiO 2 (s) + 4 H F(g)  SiF 4 (g) + 2 H 2 O (l)

42)

∆ H ° rxn = - 184 kJ

43) H ow mu ch ene rgy can be relased during the follo wing react ion if 2.50 L B2 H 6 and 5.65 L Cl 2 (Bo th gases are ini tia lly at S TP), are a llow ed t o react? B2 H 6 (g) + 6 Cl 2 (g)  2 B Cl 3 (g) + 6 H C l(g)

8

∆ H ° rxn = - 1396 kJ

43)...