CHEM EXAM 3

Enthalpy

100

How much energy is required to heat up 80 g of water from 26C to 48C? Give your answer in J.

7356 J

200

Determine the final temperature when 32.2 g of water at 14.9 °C mixes with 32.2 grams of water at 46.8 °C.

30.9 C

300

A 10 g iron bar (temp = 80C) is dropped into 70 g of water (temp = 25C). What is the final temperature? (specific heat of water is 4.184 J/gC, iron is 0.46 J/gC)

26 C

400

Consider the following reaction: 2C4H10 + 13O2 → 8CO2 + 10H2O ΔHrxn = -2044 kJ If we have a 10.8 kg sample of C4H10, calculate heat in kJ for the complete combustion of all C4H10 present.

-1.9*10^5 kJ

Energy & Calorimetry

100

If 16 J of work is being done on a system and 1016 J of heat are being gained by the surroundings, what is the total energy change of the system?

-1000 J

200

A piston has external pressure of 8.80 atm. How much work has been done if the cylinder goes from volume of 0.550 L to 0.950 L? (101.3 J = 1L*atm). Give your answer in J.

-357 J

300

A 7.0 g sample of cyclohexane (MW = 84.1 g/mol) is combusted in a bomb calorimeter with total heat capacity of 3.86 kj/C. The temp of the calorimeter increases from 20.5C to 30.8C. What is the heat combustion for the cyclohexane in kJ/mol?

-477.6 kJ/mol

400

A balloon of argon gas initially at 2.3 L transfers 485 J of heat to the surroundings. The final volume of the balloon is 2.05 L. The external pressure is 1 atm. What is the total change in energy for the system? (101.3 J = 1 atm*L)

-460 J

Hess's Law

100

C + O2 --> CO2 ΔHrxn = -3000kJ 

Based on the above information, what is the change in enthalpy for the reaction below? 

 3CO2 --> 3C + 3O2

9000 kJ

200

what is the change in enthalpy for this reaction? 2 H2S(g) + 3 O2(g) ---> 2 H2O(l) + 2 SO2(g) 

Standard enthalpies (in kJ/mol) are as follows:

H2S(g) =-20.6

H2O(g) = -285.8

H2O(l) = -241.8

SO2(g) = -296.8

-1036 kJ

300

Find the enthalpy change for this reaction, 

 {{ 2S + 3O2 → 2SO3 }} 

using the enthalpies of other reactions given: 

S + O2→ SO2 ∆H = - 297 kJ 

2SO3 → 2SO2 + O2 ∆H = 198 kJ

-792 kJ

400

Calculate ΔH for the reaction,

4 NH3 (g) + 5 O2 (g) --> 4 NO (g) + 6 H2O (g)

from the following Data: 

N2 (g) + O2 (g) --> 2NO (g) ΔH = -180.5 kJ 

N2 (g) + 3H2 (g) --> 2NH3 (g) ΔH = -91.8 kJ 

2H2 (g) + O2 (g) --> 2H2O (g) ΔH = -483.6 kJ

ΔH = -1628 kJ

500

Find the ΔH for the reaction below, 

{{ 2 Al (s) + 3 Cl2 (g) --> 2 AlCl3(s)  }} given the following reactions and subsequent ΔH values: 

2 Al (s) + 6 HCl (aq) --> 2 AlCl3 (aq) + 3 H2 (g) ΔH = -1049. kJ 

HCl (g) --> HCl (aq) ΔH = -74.8 kJ 

H2 (g) + Cl2 (g) --> 2 HCl (g) ΔH = -1845. kJ 

AlCl3 (s) --> AlCl3 (aq) ΔH = -323. kJ

-6387 kJ