Chemistry Answers

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?

Given the formula for change in internal energy, U = Q + W, calculate work for a

system that absorbs 350 kJ of heat and for which U = 150 kJ. Is the work done on

the system or by the system? Does the system expand or contract?

A sample biogas contains 10.75 mol ethane, 6.35 mol pentane and 2.89 mol propane. If the total pressure I 2. 46 atm, What are the partial pressures of the gases?

1. What is the boiling point and freezing point of a solution containing 6 g of

glycerol (C3H8O3) in 25 g of water?

2. What is the molecular mass of a solute in a solution containing 3.8 g of

nonelectrolyte in 420 g of water which freezes at -23 oC?

Identify what colligative property is applied or observed in the following. Explain

your answer.

1. Salt is mixed with ice in ice cream making.

2. Salt and sugar are used in food preservation.

3. Coolant is added to car radiators.

4. Pressure cooker.

5. Pruned or wrinkled fingers.

Solve for what is being asked.

What is the molar mass of the solute in a solution made by dissolving 34.41

g of an unknown nonelectrolyte compound in 280.0 g benzene. The boiling point of

the solution is 93.2 °C. Benzene has a boiling point of 80.1 °C and molal boiling-

point elevation constant of 2.53 °C/m.

What is the PH of a solution having the following H+ concentration?

a. 5*10^-3 M

b. 0.003M

c. 2.0*10^-6

Identify the Lewis acid in the following reaction.

a) ALCL₃ + CL^- ⤑ ALCL₄^-

b) BF₃ + NH₃ ⤑ BF₃ - NH₃

c) SiCL₄ + 2CL^- ⤑ SiCL₆^-2

d) PF₅ + F^- ⤑PF₆

In each of the reactions listed below, identify the Bronsted-lowery acids?

a. CH₃COOH (aq) + H₂O (l) CH₃COO^-(aq) + H₃0⁺ (aq)

b. HCN (aq) + SO4^-2 ↔ CN^-(aq) + HSO₄^-(aq)

c. HF (aq) + NH₃(g) ↔ F^-(aq) + NH₄⁺(aq)

d. HCIO₄(aq) + N₂H₄(aq) ↔ CIO₄^-(aq) + N₂H₅⁺(aq)

an unknown salt when heated with buses flame produced a bright-yellow flame.an aqueous solution of this salt when reacted with dilute HCl related a gas turns lime water milky. upon addition of calcium chloride solution to an aqueous solution of salt ,a white precipitate is formed. what is the unknown salt?