Chapter 5: Thermodynamics Worksheet With Answers - Ap Chemistry 2015-2016 (Page 4 of 14) in pdf

Chapter 5: Thermodynamics Worksheet With Answers - Ap Chemistry 2015-2016 Page 4

16) A g as i s c onfined t o a c ylinder w ith a p iston u nder c onstant a tmospheric p ressure ( fig. 5 .3). W hen t he

gas r eacts, i t r eleases 7 9 k J o f h eat t o i ts s urroundings a nd d oes 1 8 k J o f P -‐‑ V w ork o n i ts s urroundings.

What a re t he v alues f or ∆ H a nd ∆ E f or t his p rocess?

E = -‐‑ 9 7 k J; H = -‐‑ 7 9 k J ( see p g 1 64 e quation 5 .10 f or e xplanation)

17) T he t hermochemical e quation f or t he b urning o f o ne m ole o f b enzene u nder s tandard c onditions i s

C6H6(l) + 1 5/2 O 2(g) → 6 C O2(g) + 3 H 2O(l) ∆ H c omb = – 3267.7 k J

a. I s t his r eaction e xothermic o r e ndothermic? H ow d o y ou k now?

exothermic

b. H ow m uch h eat i s r eleased w hen a 5 .00-‐‑ g s ample o f b enzene i s b urned i n e xcess o xygen u nder

standard c onditions? ( m.w. C 6H6 = 7 8.11 g /mol)

-‐‑ 2 09 k J

18) U sed i n w elding m etals, t he r eaction o f a cetylene w ith o xygen:

C2H2(g) + 5 /2 O 2(g) → H2O(g) + 2 C O2(g)

∆H=–1255.5 k J

How m uch P V w ork i s d one ( in k ilojoules) a nd w hat i s t he v alue o f ∆ E ( in k ilojoules) f or t he r eaction o f

6.50 g o f a cetylene a t a tmospheric p ressure i f t he v olume c hange i s – 2.80 L ?

W = 0 .2828 k J; E = -‐‑ 3 12.7 k J

19) A luminum m etal r eacts w ith c hlorine w ith a s pectacular d isplay o f s parks:

2 A l(s) + 3 C l2(g) → 2 A lCl3(s)

∆H= – 1408.4 k J

How m uch h eat ( in k ilojoules) i s r eleased o n r eaction o f 5 .00 g o f A l?

-‐‑ 1 408.4 k J

5.5: C alorimetry

1. Water h as a s pecific h eat c apacity o f 4 .184 J /g·°C.

This m eans i t t akes 4 .184 J t o h eat 1 .00 g ram o f w ater 1 .00°C.

a) How m uch e nergy w ill i t t ake t o h eat 1 0.0 g rams o f w ater 1 °C? _ _____________ 4 1.84 J

b) How m uch e nergy i s n eeded t o h eat 3 0.0 g H

O f rom 1 0.0 ° C t o 5 0.0 ° C? _ ___________ 5 020 J

2. Let’s t ry a s tandard c alorimetry p roblem.

A p ot o f w ater ( 2.5 L iters o f w ater) i nitially a t 2 5.0°C i s h eated t o b oiling ( 100.°C).

How m uch e nergy ( in J ) i s n eeded t o h eat t he w ater? ( The d ensity o f w ater i s 1 g /mL.)

780000 J

What w ould t his a mount o f h eat b e i n k J? _ __________ 7 80 k J

Chapter 5: Thermodynamics Worksheet With Answers - Ap Chemistry 2015-2016 Page 4