Exam 5: Thermochemistry

What is the standard enthalpy of formation of liquid methanol,CH₃OH(l)? C(graphite)+ O₂(g)→ CO₂(g) ΔH°_rxn = -393.5 kJ/mol H₂(g)+ ½O₂→ H₂O(l) ΔH°_rxn = -285.8 kJ/mol CH₃OH(l)+ 3/2O₂(g)→ CO₂(g)+ 2H₂O(l) ΔH°_rxn = -726.4 kJ/mol

A system which does work on the surroundings with no heat change has

A system that does no work but which transfers heat to the surroundings has

Which of the following is incorrectly matched?

The heat of solution of ammonium nitrate is 26.2 kJ/mol.If a 5.368 g sample of NH₄NO₃ is added to 40.0 mL of water in a calorimeter at 23.5°C,what is the final temperature of the solution? The specific heat of water is 4.18 J/g·°C and the heat capacity of the calorimeter is 0.650 kJ/°C.

When Karl Kaveman adds chilled grog to his new granite mug,he removes 10.9 kJ of energy from the mug.If it has a mass of 625 g and was at 25°C,what is its new temperature? Specific heat capacity of granite = 0.79 J/g·°C.

Suppose a 0.500-g sample of an organic compound is analyzed via bomb calorimetry.The temperature of the calorimeter is measured over time.At t = 5 min,the combustion reaction is initiated.Below is a plot of the data that are obtained. Suppose the experiment is repeated under identical conditions,but with a 1.000-g sample of the organic compound.What might a plot of the resulting data look like?

Which represents an enthalpy change at 25 °C and 1 atm that is equal to ΔH^o_f for H₂O(l)?

A 1.00-g sample of octane (C₈H₁₈)is burned in a bomb calorimeter that has a heat capacity of 5.80 kJ/°C.The temperature of the calorimeter rises from 25.00°C to 33.20°C.What is ΔU per mole for the combustion of octane?

How much heat is released if 35.0 g of ethanol (C₂H₅OH)burns in excess oxygen? C₂H₅OH(l)+ 3O₂(g)→ 2 CO₂(g)+ 3 H₂O(l)ΔH°_rxn = -1367 kJ/mol

Ethanol,C₂H₅OH,is promoted as a clean fuel and is used as an additive in many gasoline mixtures.Calculate the ΔH°_rxn for the combustion of ethanol. Substance ΔH°_f(kJ/mol) C₂H₅OH(l)-277.0 CO₂(g)-393.5 H₂O(g)-241.8

The enthalpy of vaporization of a compound is always positive.

A piece of copper metal is initially at 100.0°C.It is dropped into a coffee cup calorimeter containing 50.0 g of water at a temperature of 20.0°C.After stirring,the final temperature of both copper and water is 25.0°C.Assuming no heat losses,and that the specific heat (capacity)of water is 4.18 J/g·°C,what is the heat capacity of the copper in J/°C?

A Snickers candy bar contains 280 Calories,of which the fat content accounts for 120 Calories.What is the energy of the fat content,in kJ? (1 cal = 4.184 J)

Pentaborane B₅H₉(s)burns vigorously in O₂ to give B₂O₃(s)and H₂O(l).What is ΔH° for the combustion of 1 mol of B₅H₉(s)? Substance ΔH°_f (kJ/mol) B₂O₃(s) -1273.5 B₅H₉(s) +73.2 H₂O(l) -285.8

Given that CaO(s)+ H₂O(l)→ Ca(OH)₂(s),ΔH°_rxn = -64.8 kJ/mol,how many grams of CaO must react in order to liberate 525 kJ of heat?

ΔH does not depend on the path of a reaction,but ΔU does.

A system contracts from an initial volume of 15.0 L to a final volume of 10.0 L under a constant external pressure of 0.80 atm.What is W? (1 L·atm = 101.3 J)

Using Hess' law,what is ΔH°_rxn at 25°C for the following reaction? ClF(g)+ F₂(g)→ ClF₃(g)2ClF(g)+ O₂(g)→ Cl2O(g)+ OF₂(g)ΔH°_rxn = +167.4kJ/mol 2ClF₃(g)+ 2O₂(g)→ Cl₂O(g)+3OF₂(g)ΔH°_rxn = +341.4kJ/mol 2F₂(g)+ O₂(g)→ 2OF₂(g)ΔH°_rxn = -43.4 kJ/mol

Natural gas,or methane,is an important fuel.Combustion of one mole of methane releases 802.3 kJ of energy.How much energy does that represent in kcal? (1 cal = 4.184 J)