Skip to main content
Pearson+ LogoPearson+ Logo
Ch.19 - Chemical Thermodynamics
Back
Previous problem
Next problem
All textbooksBrown 14th EditionCh.19 - Chemical ThermodynamicsProblem 89

Chapter 19, Problem 89

The reaction 2 Mg(s) + O2(g) ⟶ 2 MgO(s) is highly spontaneous. A classmate calculates the entropy change for this reaction and obtains a large negative value for ΔS°. Did your classmate make a mistake in the calculation? Explain.

Verified Solution
Video duration:
2m
This video solution was recommended by our tutors as helpful for the problem above.
341
views
Was this helpful?

Video transcript

Welcome back everyone in this example, we're given the reaction of formals of solid iron with three moles of oxygen gas to produce two moles of iron, three oxide. That's highly spontaneous and has a change in entropy. That can be a large negative value. Is this statement true or false and explain. So we're told that the change in entropy is a large negative value. We want to recall our second law of thermodynamics which states that the entropy of the universe is going to increase for any spontaneous process. So going back to the prompt, the entropy of our reaction being very negative is referring to the entropy of our system as a negative value. And sorry, just so that it's clear, let's scoot this over. So if we know that for any spontaneous process, which the reaction is in this case according to the prompt, it's highly spontaneous. The entropy of our universe is going to also increase with that spontaneity, then that means that it would definitely affect the entropy of our system being negative. And so for our final answer, we're going to say that the statement is true and for our explanation will say because the negative change, an entropy of our system can be offset by the change in entropy of our surroundings. And so this statement is our final answer to complete this example. I hope that everything I reviewed was clear. If you have any questions, please leave them down below and I'll see everyone in the next practice video
Previous problemNext problem
Related Practice
Textbook Question

(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.

688
views
Textbook Question

The crystalline hydrate Cd(NO3)2⋅4 H2O(s) loses water when placed in a large, closed, dry vessel at room temperature: Cd(NO3)2⋅4 H2O(s) → Cd(NO3)2(s) + 4  H2O(g) This process is spontaneous and ΔH° is positive at room temperature. (b) If the hydrated compound is placed in a large, closed vessel that already contains a large amount of water vapor, does ΔS° change for this reaction at room temperature?

367
views
Textbook Question

For each of the following processes, indicate whether the signs of ΔS and ΔH are expected to be positive, negative, or about zero. (e) A piece of charcoal is combusted to form CO2(g) and H2O(g).

793
views
Textbook Question

Consider a system that consists of two standard playing dice, with the state of the system defined by the sum of the values shown on the top faces. (f) Calculate the absolute entropy of the two-dice system.

459
views
Textbook Question

A standard air conditioner involves a refrigerant that is typically now a fluorinated hydrocarbon, such as CH2F2. An air-conditioner refrigerant has the property that it readily vaporizes at atmospheric pressure and is easily compressed to its liquid phase under increased pressure. The operation of an air conditioner can be thought of as a closed system made up of the refrigerant going through the two stages shown here (the air circulation is not shown in this diagram).

During expansion, the liquid refrigerant is released into an expansion chamber at low pressure, where it vaporizes. The vapor then undergoes compression at high pressure back to its liquid phase in a compression chamber. (c) In a central air-conditioning system, one chamber is inside the home and the other is outside. Which chamber is where, and why?

375
views
Textbook Question

A standard air conditioner involves a refrigerant that is typically now a fluorinated hydrocarbon, such as CH2F2. An air-conditioner refrigerant has the property that it readily vaporizes at atmospheric pressure and is easily compressed to its liquid phase under increased pressure. The operation of an air conditioner can be thought of as a closed system made up of the refrigerant going through the two stages shown here (the air circulation is not shown in this diagram).

During expansion, the liquid refrigerant is released into an expansion chamber at low pressure, where it vaporizes. The vapor then undergoes compression at high pressure back to its liquid phase in a compression chamber. (e) Suppose that a house and its exterior are both initially at 31 °C. Some time after the air conditioner is turned on, the house is cooled to 24 °C. Is this process spontaneous or nonspontaneous?

491
views