Question

Read and answer the following problems. Show your solutions.

1. The work done by a system is 8 J, when 40 J heat is supplied to it. What is the

change in internal energy of the system during the process?

2. Given the balanced equation below for the highly exothermic reaction of aluminum

with oxygen to form aluminum oxide:

4Al(s) + 3O2(g)  2Al2O3(s) ∆H = - 1,670 kJ

a. What is the value of ∆H when 2 moles of aluminum react?

b. What is the value of ∆H when 10.8 g of aluminum reacts?

c. A certain reaction releases 6,881 kJ of heat. What mass of aluminum oxide was

produced in the reaction?

3. From the given enthalpies of reaction;

4HCl(g) + O2(g)  2H2O(l) + 2Cl2(g) ∆Hrxn = -202.4kJ/mol

1⁄2 H2(g) + 1⁄2 F2(g) HF(l) ∆Hrxn = -600.0 kJ/mol

H2(g) + 1⁄2 O2 (g)  H2O(l) ∆Hrxn = -285.8 kJ/mol

Find:

∆Hrxn for 2HCl(g) + F2(g)  2HF(l) + Cl2(g)

Answer 1

1.Change in internal energy of the system=32J

2. a)Value of ∆H=-67kJ

b) value of ∆H=904.4 kJ

c) Mass of aluminum oxide produced=13.4g

3.2HgO (s) ------> 2 Hg(l) + O2(g) \Delta H= 181.34 KJ /mol

a) \Delta H = ? HgO = 0.750 mol

we know \Delta H =q

2 mol of HgO ------> 181.34 KJ

0.750 mol of HgO -----> X

x = 181.34 KJ * 0.750 mol of HgO / 2 mol of HgO

x = 181.34 KJ * 0.375

x = 68.00 KJ

q = 68.00 KJ /mol