Mod 5 Homework

Given the following thermochemical equation, calculate the heat involved in decomposing 12.5 g of water to the elements: 2H2(g) + O2(g) --> 2H2O(l) ΔH = -571.6 kJ

+198 kJ

Given the thermochemical equation: 2NO(g) + O2(g) --> 2NO2(g) ΔH* = -114.0 kJ, calculate ΔHo for the following reaction: NO2(g) --> NO(g) + 1/2O2(g)

+57.00 kJ

Consider the reaction in which acetylene is cyclized into benzene: 3C2H2(g) ---> C6H6(l) ΔH = -630 kJ. What would be the enthalpy for the decomposition of benzene into acetylene (i.e., the reverse reaction)?

+630 kJ

Given the thermochemical equation H2(g) + Cl2(g) --> 2HCl(g) ΔHo = -184.6 kJ, calculate ΔHo for the following reaction: HCl(g) --> 1/2H2(g) + 1/2Cl2(g)

+92.3 kJ

A 2.839-g sample of C2H4O was burned in a bomb calorimeter whose total heat capacity is 16.77 kJ/oC. The temperature of the calorimeter increases from 22.62oC to 26.87oC. What is the heat of combustion per mole of C2H4O?

-1.10 x 103 kJ/mol

Calculate the standard enthalpy of formation of solid SrCO3, given the following data: 2Sr(s) + O2(g) --> 2SrO(s) ΔH = -1184 kJ SrO(s) + CO2(g) --> SrCO3(s) ΔH = -234 kJ C(graphite) + O2(g) --> CO2(g) ΔH = -394 kJ

-1220 kJ/mol

The ΔE of a system that releases 14.4 J of heat and does 4.2 J of work on the surroundings is ________ J.

-18.6

For the following reaction, what is the enthalpy of cyclization per mole of acetylene? 3C2H2(g) ---> C6H6(l) ΔH = -630 kJ

-210 kJ/mol C2H2

From the following enthalpies of reaction, H2(g) + F2(g) --> 2HF(g) ΔH = -537 kJ C(s) + 2F2(g) --> CF4(g) ΔH = - 680 kJ 2C(s) + 2H2(g) --> C2H4(g) ΔH = +52.3 kJ calculate ΔH for the reaction of ethylene with F2: C2H4(g) + 6F2(g) --> 2CF4(g) + 4HF(g)

-2486 kJ

A 2.20-g sample of quinone, C6H4O2, is burned in a bomb calorimeter whose total heat capacity is 7.854 kJ/oC. The temperature of the calorimeter increases from 23.44oC to 30.57oC. What is the heat of combustion per gram of quinone? Per mole of quinone? (Molecular weight of quinone is 108.1.)

-25.5 kJ/g, -2750 kJ/mol

Use the following thermochemical equations: C2H2(g) + 5/2O2(g) --> 2CO2(g) + H2O(g) ΔHo = -1300 kJ C2H6(g) + 7/2O2(g) --> 2CO2(g) + 3H2O(g) ΔHo = -1560 kJ H2(g) + 1/2O2(g) --> H2O(g) ΔHo = -286 kJ to calculate ΔHo for the following reaction: C2H2(g) + 2H2(g) --> C2H6(g)

-312 kJ

Given the equation: 2SO3(g) --> 2SO2(g) + O2(g) ΔH? = +198.2 kJ, and that the heat of formation of gaseous sulfur dioxide is -296.8 kJ/mol, what is the heat of formation of gaseous sulfur trioxide in kJ/mol?

-395.9

Suppose you are given the following hypothetical reactions: X --> Y ΔH = -80 kJ X --> Z ΔH = -125 kJ Use Hess's law to calculate the enthalpy change for the reaction Y --> Z.

-45 kJ

When 0.215 mol NH3 is formed from nitrogen and hydrogen, 9.91 kJ of energy is released as heat. Assuming constant pressure is maintained, what is the H for this reaction per mole of NH3 formed

-46.1 kJ

From the following heats of reaction: 2C(graphite) + 2H2(g) + O2(g) --> 2H2CO(g) ΔH = -217 kJ 2C(graphite) + 2H2(g) + 2O2(g) --> 2H2CO2(l) ΔH = -849 kJ, calculate the heat for the reaction: 2H2CO(g) + O2(g) --> 2H2CO2(l)

-632 kJ

A common unit of energy is the erg, 1 g-cm2/s2. How many ergs are there in 1 J?

1 x 107 ergs

Consider the following reaction: 2Na(s) + Cl2(g) --> 2NaCl(s) ΔH = -821.8 kJ What is the amount of heat transferred when 5.6 g of Na(s) reacts at constant pressure?

1.0 x 102 kJ

Calculate the kinetic energy of a 7.3-kg steel ball traveling at 18.0 m/s.

1.2 x 103 J

A sample of aluminum absorbed 9.86 J of heat, and its temperature increased from 23.2°C to 30.5°C. What was the mass of the aluminum sample? (The specific heat of aluminum is 0.90 J/g-K.)

1.5 g

Calculate the change in internal energy of the system and determine whether the process is endothermic or exothermic for a chemical reaction in which 10.0 kJ of heat is absorbed while the system does no work on the surroundings.

10.0 kJ, endothermic

Consider the following reaction: 2C2H2(g) + 5O2(g) --> 4CO2(g) + 2H2O(g) ∆H = -2511 kJ Calculate the amount of heat transferred when 2.60 g of C2H2(g) is consumed in this reaction at constant pressure

126 kJ

Calculate the change in internal energy of the system for the following process: A balloon is heated by adding 320 J of heat. It expands, doing 180 J of work on the atmosphere.

140 J

From the following heats of reaction: N2(g) + 2O2(g) --> 2NO2(g) ΔH = +67.6 kJ 2NO(g) + O2(g) --> 2NO2(g) ΔH = -113.2 kJ calculate the heat of the reaction: N2(g) + O2(g) --> 2NO(g)

180.8 kJ

At 0oC the average velocity of CH4 molecules in air is 600. m/s. What is the total kinetic energy of 1.00 mol of CH4 molecules moving at this speed?

2.88 x 103 J

The value of H° for the following reaction is -126 kJ. Determine the amount of heat (in kJ) that would be evolved by the reaction of 25.0 g of Na2O2 with water. 2Na2O2(s) + 2H2O(l) --> 4NaOH(s) + O2(g)

20.2 kJ

The heat capacity of lead is 0.13 J/g.°C. How many joules of heat would be required to raise the temperature of 15 g of lead from 22°C to 37°C?

29

Which one of the following reactions has a positive value of ΔH°?

2H2O(l) --> 2H2(g) + O2(g)

Consider the following thermochemical equation: CH4(g) + I2(g) --> CH3I(g) + HI(g) ΔH = +23 kJ What energy change occurs when 1.6 mol of CH4 reacts?

37 kJ is absorbed.

How much heat is needed to raise the temperature of 75.2 mol of water (heat capacity of 4.184 J/g-1-K-1) from 12.5oC to 80.0oC?

382 kJ

For which one of the following reactions is the value of ΔH° not equal to ΔHf° for the product?

3Mg(s) + N2(l) --> Mg3N2(s

What is the number of J in a Btu? (See the hint for the definition of a Btu.)

454 x 4.184/1.8 = 1055

A 1.55-g sample of propane, C3H8, was burned in a bomb calorimeter whose total heat capacity is 12.3 kJ/oC. The temperature of the calorimeter plus its contents increased from 21.36oC to 27.69oC. What is the heat of combustion per gram of propane?

50.2 kJ/g

A volume of 50.0 mL of 0.400 M HBr at 24.35oC is added to 50.0 mL of 0.400 M NaOH, also at 24.35oC. The final temperature is 27.06oC. Calculate the enthalpy change, ΔH, in kJ for the following reaction:HBr(aq) + NaOH(aq) --> NaBr(aq) + H2O(l) (Heat capacity of the system is 0.418 kJ/?C.)

56.7

If the heat capacity of a ceramic cup is 0.820 J/oC, how much heat is required to raise the temperature of the cup from 25.0oC to 100.0oC?

61.5 J

A 15.0-g block of aluminum at an initial temperature of 27.5oC absorbs 0.678 kJ of heat. What is the final temperature of the block? (The specific heat of Al is 0.902 J/g-1-oC-1.)

77.6°C

Calculate the kinetic energy of a 13.3-kg steel ball traveling at 12.0 m/s.

9.6 x 102 J

Which of the following is true if work has been performed on a system

An object in the system must have been moved against a force

Which statement is not correct Heat and work are state functions

Heat and work are state functions

Which one of the following is true concerning enthalpy?

It is a state function

An endothermic reaction is carried out in a coffee-cup calorimeter. Which statement is incorrect for this process?

The enthalpy change for the reaction is equal to qH2O

Which of the following changes always results in a negative ΔE?

The system gives off heat and does work.

When heat is absorbed by the system from the surroundings, the process is said to be ____________, and the sign of qprocess is ___________

endothermic, positive

According to the first law of thermodynamics

energy is conserved during any process.

Which of the following quantities - heat, work, enthalpy, internal energy - depend only on the end points and not on the path followed in a process?

enthalpy and internal energy

For a process in which the internal energy does not change, which of the following are possible? (i) heat > 0, work < 0 (ii) heat > 0, work > 0 (iii) heat < 0, work < 0 (iv) heat < 0, work > 0

i and iv only

Natural gas is composed primarily of

methane.

The fuel used in spacecraft must contain as much energy per gram of material as possible. Based on this consideration only, which of the following fuels is best suited to be a spacecraft fuel? (i) dimethylhydrazine, (CH3)2NNH2 ΔHcombustion = -1694 kJ/mol (ii) methanol, CH3OH ΔHcombustion = -726 kJ/mol (iii) ethanol, C2H5OH ΔHcombustion = -1371 kJ/mol (iv) octane, C8H18 ΔHcombustion = -5500 kJ/mol (v) ethylene glycol, C2H6O2 ΔHcombustion = -1190 kJ/mol

octane