AP Chemistry Unit 6

Using the following thermochemical data, calculate ΔHf° of Ga2O3(s). 2GaCl3(s) + 3H2O(l) → Ga2O3(s) + 6HCl(g) ΔH° = 263.9 kJ/mol 2Ga(s) + 3Cl2(g) → 2GaCl3(s) ΔH° = -1049.4 kJ/mol 4HCl(g) + O2(g) → 2Cl2(g) + 2H2O(l) ΔH° = -202.4 kJ/mol

-1089.1 kJ/mol

Consider the following processes: ΔH (kJ/mol) 3B → 2C + D -125 (1/2)A → B 150 E + A → D 350 Calculate ΔH for: B → E + 2C

-175 kJ/mol

When 0.262 mol of a weak base (A-) is reacted with excess HCl, 6.91 kJ of energy is released as heat. What is ΔH for this reaction per mole of A- consumed?

-26.4 kJ

2 NH3(g) → 3 H2(g) + N2(g) ΔH°rxn = 92 kJ/molrxn According to the information above, what is the standard enthalpy of formation, ΔH°f , for NH3(g) at 298 K ?

-46 kJ/mol

Given the heats of the following reactions: ΔH°(kJ) I.P4(s) + 6Cl2(g) → 4PCl3(g) -1225.6 II.P4(s) + 5O2(g) → P4O10(s) -2967.3 III. PCl3(g) + Cl2(g) → PCl5(g) -84.2 IV.PCl3(g) + O2(g) → Cl3PO(g) -285.7 Calculate the value of ΔH° for the reaction below: P4O10(s) + 6PCl5(g) → 10Cl3PO(g)

-610.1 kJ

A 175.0 g sample of metal at 90.0° C is added to 175.0 g of H2O at 20.0° C. The temperature of the water rises to 30.9° C. Assuming that the calorimeter is a perfect insulator, calculate the specific heat of the metal in J/g° C. (Specific heat of H2O is 4.18 J/g° C.)

0.771

Which of the following processes is (are) exothermic? F (g) + e -> F- (g) 2F (g) F2 -> (g) Li+ (g) + e Li -> (g)

1, 2, 3 **

Which of the following species would need to appear in an Enthalpies of Formation Table? O (g) O2 (g) O2 (l) Hg (l) Hg (s)

1, 3, 5 only

Using the following thermochemical data: 2Y(s) + 6HF(g) → 2YF3(s) + 3H2(g)ΔH° = -1811.0 kJ/mol2Y(s) + 6HCl(g) → 2YCl3(s) + 3H2(g)ΔH° = -1446.2 kJ/mol calculate ΔH° for the following reaction:YF3(s) + 3HCl(g) → YCl3(s) + 3HF(g)

182.4 kJ/mol

Using the following data, calculate the heat of reaction for the reaction 2 C(s) + 2 H2O CH4(g) + CO2(g) C(s) + H2O(g) CO(g) + H2(g) ΔH° = 139.7 kJ CO2(g) + H2(g) CO(g) + H2O(g) ΔH° = 44.5 kJ CH4(g) + H2O(g) CO(g) + 3H2(g) ΔH° = 212.4 kJ

22.5

The specific heat of sodium is 1.225 J/gº C. If 672 J of heat is added to a 278 g piece of sodium at 21.4° C, what is the final temperature of the sodium?

23.4 C

The ΔH value for the reaction 1/2 O2 (g) + Hg (l) -> HgO (s) is -90.8 kJ. How much heat is released when 88.1 g Hg is reacted with oxygen?

39.9 kJ

Nitroglycerin is a very powerful explosive which decomposes to four different gases when it is detonated. 2C3H5(NO3)3(l) 3N2(g) + ½O2(g) + 6CO2(g) +5H2O(g) ΔH°f (kJ / mol) C3H5(NO3)3(l) -364 CO2(g) -393.5 H2O(g) -241.8 The heat for the reaction above is

5(-241.8) + 6(-393.5) + 2(364) kJ

A 4.1-g sample of Colorado oil shale is burned in a bomb calorimeter, which causes the temperature of the calorimeter to increase by 5.0°C. The calorimeter contains 1.00 kg of water (heat capacity of H2O = 4.184 J/g°C) and the heat capacity of the empty calorimeter is 0.10 kJ/°C. About how much heat is released per gram of oil shale when it is burned?

5.2 kJ/g

CH4(g) + 4Cl2(g) → CCl4(g) + 4HCl(g), ΔH = -434 kJ Based on the above reaction, what energy change occurs when 1.2 moles of methane (CH4) reacts?

5.2 × 105 J are released

A hot iron ball is dropped into a 200. g sample of water initially at 50°C. If 8.4 kJ of heat is transferred from the ball to the water, what is the final temperature of the water? (The specific heat of water is 4.2 J/(g·°C).)

60 C

½ H2(g) + ½ I2(s) → HI(g) ∆H = 26 kJ/molrxn ½ H2(g) + ½ I2(g) → HI(g) ∆H = -5.0 kJ/molrxn Based on the information above, what is the enthalpy change for the sublimation of iodine, represented below? I2(s) → I2(g)

62 kJ/mol rxn

Which criteria are consistent for a reaction that corresponds to standard enthalpy of formation? The reactants must be in their natural states The reactants must be pure elements. The products must have a coefficient of 1

All

For a classroom demonstration, a chemistry teacher puts samples of two different pure solid powders in a beaker. The teacher places the beaker on a small wooden board with a wet surface, then stirs the contents of the beaker. After a short time the students observe that the bottom of the beaker is frozen to the wood surface. The teacher asks the students to make a claim about the observation and to justify their claims. Which of the following is the best claim and justification based on the students' observation?

An endothermic chemical change occurred because the temperature of the beaker and the water on the board decreased as heat was absorbed by the reaction

If the same amount of heat is added to 100.0 g samples of each of the metals, all metals start at the same temperature, which metal will have the lowest temperature in the end?

Be

A 47.4 g sample of a metal is heated to 95.2°C and then placed in a calorimeter containing 120.0 g of water (c = 4.18 J/g°C) at 21.5°C. The final temperature of the water is 24.5°C. Which metal was used?

Iron (c = 0.45 J/g°C)

Given the following specific heats of metals, if the same amount of heat is added to 100.0 g samples of each of the metals, all metals start at the same temperature, which metal will have the highest temperature in the end?

Sr

In the lab, you mix two solutions (each originally at the same temperature) and the temperature of the resulting solution decreases. Which of the following is true?

The chemical reaction is absorbing energy

On a cold winter day, a steel metal fence post feels colder than a wooden fence post of identical size because:

The specific heat capacity of steel is lower than the specific heat capacity of wood

Consider the reaction H2(g) + O2(g) → H2O(l) ΔH° = -286 kJ Which of the following is true?

Two of the other answers are true

What is the sign on enthalpy for an endothermic reaction?

positive

Given the following two reactions at 298 K and 1 atm, which of the statements is true? 1.N2(g) + O2(g) → 2NO(g)ΔH1 2.NO(g) + O2(g) → NO2(g)ΔH2

ΔHf° for NO2(g) = ΔH2 + ΔH1

Which process involves the largest energy change for one mole of 1,4 dichlorobenzene, moth balls?

ΔHsublimation