8. Thermochemistry

Which of the following represents a state function?

Which of the following processes must always result in a net increase in internal energy of the system?

Consider the accompanying energy diagram. (a) Does this diagram represent an increase or decrease in the internal energy of the system?

For which of the following reactions are ΔE and ΔH equal? (a) CO2(g) + H2O(l) → H2CO (b) 2 NaHCO3 (s) → Na2CO3(s) + H2O(g) + CO2(g) (c) 2 H2(g) + O2(g) → 2 H2O(g) (d) CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g)

The diagram shows four states of a system, each with different internal energy, E. (c) Write an expression for the difference in energy between State C and State D.

The diagram shows four states of a system, each with different internal energy, E. (a) Which of the states of the system has the greatest internal energy?

In the accompanying cylinder diagram, a chemical process occurs at constant temperature and pressure. (a) Is the sign of w indicated by this change positive or negative?

Consider a process in which an ideal gas changes from state 1 to state 2 in such a way that its temperature changes from 300 K to 200 K. (c) Does the change in the internal energy, ΔE, depend on the particular pathway taken to carry out this change of state?

(c) By what means can the internal energy of a closed system increase?

Calculate E and determine whether the process is endothermic or exothermic for the following cases: (a) q = 0.763 kJ and w = -840 J.

A gas is confined to a cylinder fitted with a piston and an electrical heater, as shown here:

Suppose that current is supplied to the heater so that 100 J of energy is added. Consider two different situations. In case (1) the piston is allowed to move as the energy is added. In case (2) the piston is fixed so that it cannot move. (a) In which case does the gas have the higher temperature after addition of the electrical energy?

For the isothermal expansion of a gas into a vacuum, ΔE = 0, q = 0, and w = 0. (b) Explain why no work is done by the system during this process.

During a deep breath, our lungs expand about 2.0 L against an external pressure of 101.3 kPa. How much work is involved in this process (in J)?

How much work (in J) is involved in a chemical reaction if the volume decreases from 33.6 L to 11.2 L against a constant pressure of 90.5 kPa?

Redraw the following diagram to represent the situation (b) when work has been lost by the system.

A reaction is carried out in a cylinder fitted with a movable piston. The starting volume is V = 5.00 L, and the appa- ratus is held at constant temperature and pressure. Assum- ing that ∆H = -35.0 kJ and ∆E = -34.8 kJ, redraw the piston to show its position after reaction. Does V increase, decrease, or remain the same?

Which statement is true of the internal energy of a system and its surroundings during an energy exchange with a negative ΔEsys? a. The internal energy of the system increases and the internal energy of the surroundings decreases. b. The internal energy of both the system and the surroundings increases. c. The internal energy of both the system and the surroundings decreases. d. The internal energy of the system decreases and the internal energy of the surroundings increases.

A gas is confined to a cylinder under constant atmospheric pressure, as illustrated in Figure 5.4. When 0.49 kJ of heat is added to the gas, it expands and does 214 J of work on the surroundings. What are the values of H and E for this process?

Identify each energy exchange as primarily heat or work and determine whether the sign of ΔE is positive or negative for the system. a. Sweat evaporates from skin, cooling the skin. (The evaporating sweat is the system.) b. A balloon expands against an external pressure. (The contents of the balloon is the system.) c. An aqueous chemical reaction mixture is warmed with an external flame. (The reaction mixture is the system.) Identify energy exchanges as primarily heat or work. Determine whether the sign of E is positive or negative for the system.

Identify each energy exchange as primarily heat or work and determine whether the sign of ΔE is positive or negative for the system. a. Sweat evaporates from skin, cooling the skin. (The evaporating sweat is the system.) b. A balloon expands against an external pressure. (The contents of the balloon is the system.) c. An aqueous chemical reaction mixture is warmed with an external flame. (The reaction mixture is the system.) Identify energy exchanges as primarily heat or work.

A system releases 622 kJ of heat and does 105 kJ of work on the surroundings. What is the change in internal energy of the system?

A system absorbs 196 kJ of heat and the surroundings do 117 kJ of work on the system. What is the change in internal energy of the system?

The air in an inflated balloon (defined as the system) warms over a toaster and absorbs 115 J of heat. As it expands, it does 77 kJ of work. What is the change in internal energy for the system?

What is internal energy?

Calculate the work done in joules by a chemical reaction if the volume increases from 3.2 L to 3.4 L against a constant external pressure of 3.6 atm. What is the sign of the energy change?

How much work (in J) is required to expand the volume of a pump from 0.0 L to 2.5 L against an external pressure of 1.1 atm?

The average human lung expands by about 0.50 L during each breath. If this expansion occurs against an external pressure of 1.0 atm, how much work (in J) is done during the expansion?

The air within a piston equipped with a cylinder absorbs 565 J of heat and expands from an initial volume of 0.10 L to a final volume of 0.85 L against an external pressure of 1.0 atm. What is the change in internal energy of the air within the piston?

A reaction inside a cylindrical container with a movable RAN piston causes the volume to change from 12.0 L to 18.0 L while the pressure outside the container remains constant at 0.975 atm. (The volume of a cylinder is V = pr2h, where h is the height; 1 L # atm = 101.325 J.) (a) What is the value in joules of the work w done during the reaction?

A reaction inside a cylindrical container with a movable RAN piston causes the volume to change from 12.0 L to 18.0 L while the pressure outside the container remains constant at 0.975 atm. (The volume of a cylinder is V = pr2h, where h is the height; 1 L # atm = 101.325 J.) (b) The diameter of the piston is 17.0 cm. How far does the piston move?

A gas is compressed from an initial volume of 5.55 L to a final volume of 1.22 L by an external pressure of 1.00 atm. During the compression the gas releases 124 J of heat. What is the change in internal energy of the gas?

At a constant pressure of 0.905 atm, a chemical reaction takes place in a cylindrical container with a movable piston having a diameter of 40.0 cm. During the reaction, the height of the piston drops by 65.0 cm. (The volume of a cylinder is V=pr2h,wherehistheheight;1Latm=101.3J.) (b) What is the value in joules of the work w done during the reaction?

At a constant pressure of 0.905 atm, a chemical reaction takes place in a cylindrical container with a movable piston having a diameter of 40.0 cm. During the reaction, the height of the piston drops by 65.0 cm. (The volume of a cylinder is V=pr2h,wherehistheheight;1Latm=101.3J.) (a) What is the change in volume in liters during the reaction?

When 1 mol of a fuel burns at constant pressure, it produces 3452 kJ of heat and does 11 kJ of work. What are ΔE and ΔH for the combustion of the fuel?

When a sample of a hydrocarbon fuel is ignited and burned in oxygen, the internal energy decreases by 7.20 kJ. If 5670 J of heat were transferred to the surroundings, what is the sign and magnitude of work? If the reaction took place in an environ- ment with a pressure of 1 atm, what was the volume change?

The change in internal energy for the combustion of 1.0 mol of octane at a pressure of 1.0 atm is 5084.3 kJ. If the change in enthalpy is 5074.1 kJ, how much work is done during the combustion?

What is the difference between the internal energy change ∆E and the enthalpy change ∆H? Which of the two is mea- sured at constant pressure and which at constant volume?

Under what circumstances are ΔE and ΔH essentially equal?

The enthalpy change for the reaction of 50.0 mL of ethylene with 50.0 mL of H2 at 1.5 atm pressure (Problem 9.51) is ∆H = -0.31 kJ. What is the value of ∆E?

Assume that a particular reaction evolves 244 kJ of heat and that 35 kJ of PV work is gained by the system. What are the values of ∆E and ∆H for the system? For the surroundings?

What is the enthalpy change (ΔH) for a reaction at a constant pressure of 1.00 atm fi the internal energy chagne (ΔE) is 44.0 kJ and the volume increase is 14.0 L? (1 L-atm = 101.325 J)

A reactiont akes place at a constant pressure of 1.10 atm with an internal energy change (ΔE) of 71.5 kJ and a volume decrease of 13.6 L. What is the enthalpy change (ΔH) for the reaction? (1 L-atm = 101.325 J)

(d) For a reversible isothermal process, write an expression for ΔE in terms of q and w and an expression for ΔS in terms of q and T.

The kinetic energy of a rolling billiard ball is given by KE = 12 mv2. Suppose a 0.17-kg billiard ball is rolling down a pool table with an initial speed of 4.5 m/s. As it travels, it loses some of its energy as heat. The ball slows down to 3.8 m/s and then collides head-on with a second billiard ball of equal mass. The first billiard ball completely stops and the second one rolls away with a velocity of 3.8 m>s. Assume the first billiard ball is the system. Calculate q.

A sample of gas is contained in a cylinder-and-piston arrangement. There is an external pressure of 100 kPa. The gas undergoes the change in state shown in the drawing. (b) Now assume that the cylinder and piston are made up of a thermal conductor such as a metal. During the state change, the cylinder gets colder to the touch. What is the sign of q for the state change in this case? Describe the difference in the state of the system at the end of the process in the two cases. What can you say about the relative values of E?

A 20.0-L volume of an ideal gas in a cylinder with a piston is at a pressure of 3.0 atm. Enough weight is suddenly removed from the piston to lower the external pressure to 1.5 atm. The gas then expands at constant temperature until its pressure is 1.5 atm. Find w.

Ethyl chloride 1C2H5Cl2, a substance used as a topical anes-thetic, is prepared by reaction of ethylene with hydrogen chloride: C2H41g2 + HCl1g2 ¡ C2H5Cl1g2 ΔH° = - 72.3 kJ How much PV work is done in kilojoules, and what is the value of ΔE in kilojoules if 89.5 g of ethylene and 125 g of HCl are allowed to react at atmospheric pressure and the volume change is - 71.5 L?

Classify the following by the sign of δe for the system.

Which statement is true of the internal energy of a system and its surroundings during an energy exchange with a negative δusys ?