Question 1

All of the following statements are correct EXCEPT

Accepted Answer

The statement "if a reaction occurs at constant pressure, w = ΔE" is incorrect. At constant pressure, the work done by the system is given by w = -PΔV, where ΔV is the change in volume. Therefore, the correct statement is "if a reaction occurs at constant pressure, ΔE = q - PΔV".

Question 2

Calculate ΔE of a gas for a process in which the gas evolves 24 J of heat and has 9 J of work done on it.

Accepted Answer

The answer of Calculate ΔE of a gas for a...

Question 3

Calculate ΔE of a gas for a process in which the gas absorbs 25 J of heat and does 7 J of work by expanding.

Accepted Answer

ΔE = q - w
ΔE = 25 J - (-7 J)  [work done by the system is negative]
ΔE = 25 J + 7 J
ΔE = 32 J
The gas absorbs 25 J of heat and does a positive work of 7 J, so the internal energy of the gas increases by 32 J. Therefore, the correct answer is option C.

Question 4

Calculate ΔE of a gas for a process in which the gas evolves 8 J of heat and does 16 J of work by expanding.

Accepted Answer

The answer of Calculate ΔE of a gas for a...

Question 5

You decide to go on a diet to lose 5 lbs (1 lb = 454 g).Fatty tissue consists of about 85% fat and 15% water.In order to lose that much weight how many Calories (kcal)must be eliminated from your normal intake? Fat contains 9.0 kcal/g.

Accepted Answer

To lose 5 lbs (2270 g), considering fatty tissue is 85% fat, the fat weight to lose is 2270 g * 0.85 = 1929.5 g. Since fat contains 9.0 kcal/g, the total calories to eliminate are 1929.5 g * 9.0 kcal/g = 17365.5 kcal, rounded to 17365 kcal.

Question 6

How many kJ are equal to 3.27 L⋅atm of work?

Accepted Answer

To convert L⋅atm to kJ, use the conversion factor 1 L⋅atm = 101.325 J. Therefore, 3.27 L⋅atm = 3.27 * 101.325 J = 331.34 J, which is equal to 0.331 kJ.

Question 7

The first law of thermodynamics states that

Accepted Answer

The first law of thermodynamics, also known as the law of conservation of energy, states that the total energy change of a system is equal to the sum of the heat absorbed and the work done on the system. It does not make any statement about the pathway of the heat or work. Therefore, options A and B are incorrect. The correct answer is C.

Question 8

In which of the reactions below is ΔH an enthalpy of formation?

Accepted Answer

Enthalpy of formation refers to the change in enthalpy that occurs during the formation of one mole of a compound from its constituent elements. In reaction D, CuI is formed from its constituent elements Cu and I2, making ΔH an enthalpy of formation. The other reactions do not have ΔH as an enthalpy of formation as they involve the formation of compounds from elements and/or compounds.

Quiz 8: Thermochemistry