Exam 5: Thermochemistry: Energy Changes in Reactions

A 150 g piece of iron (C_P = 25.09 J/(mol .°C)) was heated to a temperature of 47°C and then placed in contact with a 275 g piece of copper at 20°C (C_P = 25.46 J/(mol .°C)). What was the final temperature of the two pieces of metal?

To cool your 250 mL of coffee at 90°C, you put a 100 g metal spoon in a glass of ice water to lower its temperature to 0°C, and then you put the spoon in the coffee. After thermal equilibrium has been reached, what is the final temperature of your coffee? Assume energy is exchanged only between the spoon and the coffee. The heat capacity of the metal spoon is 80 J/°C. Assume the specific heat and density of coffee are the same as that of water, 4.18 J/(g . °C) and 1.00 g/mL.

Which of the following fuels has the lowest fuel value (kJ/g)?

Ethanol (CH₃CH₂OH) has been suggested as an alternative fuel source. Ethanol's enthalpy of combustion is $\Delta$ H_comb = -1,368 kJ/mol, and its density is 0.789 g/mL. What is the fuel density of ethanol (kJ/mL)?

Ethanol (CH₃CH₂OH) has been suggested as an alternative fuel source. Ethanol's enthalpy of combustion is $\Delta$ H_comb = -1,368 kJ/mol, and its density is 0.789 g/mL. What is the fuel value of ethanol (kJ/g)?

In an experiment, 10.0 g of ice at -20°C is converted into steam with a temperature of 110°C. How much energy is required for this process? $\Delta$ H_vap = 2,260 J/g; $\Delta$ H_fus = 334 J/g; c_s(ice) = 2.06 J/(g . °C); c_s(water) = 4.18 J/(g . °C); C_s(steam) = 1.99 J/(g . °C))

The capacity to do work is a definition of ________

According to Coulomb's law, which ionic compound A-D has the smallest electrostatic potential energy (i.e., closest to zero)? The size of the anion increases in the order F < Cl < Br < I.

The energy content of a Big Mac is 540 Cal. How much water can be heated from 20°C to 90°C by this amount of energy? (c_P(water) = 1.00 g/mL, c_s(water) = 4.18 J/(g . °C), 1 Cal = 1,000 cal = 4.184 kJ)

Which statement A-D about a state function is not correct?

Explain what is meant by the term state function, and give an example of something that is a state function and something that is not a state function.

Sports trainers use cold packs containing ammonium nitrate for injured athletes. Calculate the change in temperature when 47 g of ammonium nitrate (NH₄NO₃, 80.1 g/mol) dissolves in 100 g water. Assume the specific heat of the solution is 4.5 J/(g .°C). NH₄NO₃(s) $\rightarrow$ NH₄⁺(aq) + NO₃^-(aq) $\Delta$ H = 21.1 kJ/mol

Which of the changes, A-D, will always increase the internal energy of a system?

Coal is converted into cleaner, more transportable fuels by burning it with oxygen to produce carbon monoxide. The carbon monoxide then is reacted with hydrogen using a catalyst to produce methane and water. Is the reaction between CO and H₂ exothermic or endothermic, and what is the change in enthalpy for it? The enthalpies of formation of the reactants and products are given below. Molecule \circ in kJ/mol -110 0 -75 -242

Indicate which of the following is not an element in its standard state at 25°C and 1 atm.

Use the following information to determine the standard enthalpy change when 1 mol of PbO(s) is formed from lead metal and oxygen gas. PbO(s) + C(graphite) $\rightarrow$ Pb(s) + CO(g) $\Delta$ H^o = 107 kJ 2C(graphite) + O₂(g) $\rightarrow$ 2CO(g) $\Delta$ H^o = -222 kJ

During the expansion of steam inside the cylinder of a steam engine, the piston moves and the volume of the cylinder increases by 45 mL. The external pressure is a constant 4 atm. Calculate the change in the energy (in joules) of the steam caused by doing this work. Conversion factors are provided on the information page.

Fuel value is ________

If steam expands in the cylinder of a steam engine and does 750 J of work on the surroundings and simultaneously there is 250 J of energy transferred into the steam from the surroundings, what is the change in energy of the steam?

The following diagrams illustrate the flow of energy (q) and work (w) in different processes. Which one is definitely an exothermic process?