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August 13, 2013 By Sales

DAT Chemistry Tip: How To Solve Gibbs Free Energy Problems

Gibbs free energy problems are one of those tricky questions that will most likely be tested on your DAT exam.

Here’s a question to test your knowledge of Gibbs free energy:

Which of the following is true about a spontaneous, exothermic reaction?

A. ΔG is positive
B. ΔS is positive
C. ΔS is negative
D. ΔH is positive

Don’t stress out if you can’t answer this question right now. Once you understand the concepts given below, you will to be able to solve this problem on the DAT exam very easily.

And oh yeah, this question will most likely show up on your DAT test. So make sure you understand this concept!

So What Is Gibbs Free Energy?

This is what wikipedia says:

“In thermodynamics, the Gibbs free energy (IUPAC recommended name: Gibbs energy or Gibbs function; also known as free enthalpy[1] to distinguish it from Helmholtz free energy) is a thermodynamic potential that measures the “useful” or process-initiating work obtainable from a thermodynamic system at a constant temperature and pressure (isothermal, isobaric)”

It’s something we don’t need to know. Sure if you love chemistry so much, you might want to understand this and other information on wikipedia to satisfy your appetite, but for our purposes, let’s just focus on what’s important here.

→ Gibbs free energy ΔG, is the energy that’s available to do useful work for a chemical reaction. ΔG helps us determine whether a given reaction is spontaneous or not.

Change in Gibbs Free Energy:

ΔG = ΔH – T ΔS

You must memorize this equation!

Here’s a mnemonic: Goose Hunters Take Shot Guns

If ΔG < 0, reaction is spontaneous.
If ΔG = 0, reaction is at equilibrium.
If ΔG > 0, reaction is non-spontaneous.

So how can we know when ΔG < 0 or ΔG > 0 ?

Let’s look at the equation first: ΔG = ΔH – T ΔS

Here are the different scenarios:

  • If ΔH is negative and ΔS is positive, ΔG will be negative. Thus, reaction is spontaneous.
  • If ΔH is positive and ΔS is negative, ΔG will be positive. Thus, reaction is non-spontaneous.
  • If ΔH is positive and ΔS is positive, ΔG will be negative at high temperatures (T) and ΔG will positive at low temperatures (T). Thus, the reaction can be spontaneous or non-spontaneous depending on temperature.
  • If ΔH is negative and ΔS is negative, ΔG will be positive at high temperatures (T) and ΔG will negative at low temperatures (T). Thus, the reaction can be spontaneous or non-spontaneous depending on temperature.

The chart below summarizes the points written above:

ΔHΔSΔG
Negative (-)Positive (+)Negative (-)
Positive (+)Negative (-)Positive (+)
Positive (+)Positive (+)Negative (-) at high T and Positive (+) at low T
Negative (-)Negative (-)Positive (+) at high T and Negative (-) at low T
If ΔG < 0, then reaction is spontaneous.
If ΔG = 0, then reaction is at equilibrium.
If ΔG > 0, then reaction is non-spontaneous.

So let’s review the question from the beginning of this post:

Which of the following is true about a spontaneous, exothermic reaction?

A. ΔG is positive
B. ΔS is positive
C. ΔS is negative
D. ΔH is positive

By looking at the chart, we see that only possible scenario is Answer choice B. For a reaction to be a spontaneous in a exothermic reaction (ΔH < 0), ΔS must be positive.

Filed Under: dat chemistry, dat exam, dat prep Tagged With: dat chemistry, dat prep

July 19, 2013 By Sales

How is the DAT scored?

The DAT is scored on a scale of 1 to 30. However, it is not a linear scoring system.

A 20 on a section doesn’t mean you answered one third of the questions incorrectly, but in fact you may have answered 90% of the questions correctly.

Your score is based on the number of questions you answered correctly in comparison to others who answered questions correctly. It is then calculated through CDA’s proprietary formula.

Each section is scored individually and then groups of sections are scored collectively.

The standard score of 15 signifies average performance on a national basis.

You will receive 6 scores on the DAT:

Biology
Chemistry
Reading Comprehension
Total Science (TS)
Academic Average (AA)
Perceptual Ability Test (PAT)

TS = Total Science. Weighted Average from Biology and Chemistry.

AA = Academic Average. Weighted Average from Biology, Chemistry, Reading Comprehension and Perceptual Ability Test.

PAT = Perceptual Ability Test (angle discrimination, form development, cubes, orthographic projections and apertures)

Filed Under: canadian dat, dat exam, dat scores Tagged With: canadian dat, dat exam, dat scores

July 12, 2013 By Sales

Join A Pre-Dental Student Club

You should join the pre-dental student club at your University.

Usually, the pre-dental student clubs hold mock DAT exams. These mock DAT exams can help you prepare for the exam day since you first-hand experience what it feels like to be examined with a proctor in the room. This is a better option than practicing yourself because you won’t be able to ‘cheat’ or take regular breaks.

Another benefit is that pre-dental clubs invite Dental students to give tips on how they prepared for the DAT exam. They also share their experiences of being a Dental student and what you should expect when you get into Dental school.

Filed Under: canadian dat, dat exam, dental school, pre-dental club Tagged With: canadian dat, dat exam, pre-dental club

May 7, 2013 By Sales

Don’t Make This Mistake

One of the reasons some students don’t perform well on the Dental Aptitude Test is because they don’t study from DAT preparation materials that are up-to-date.

The syllabus covered on the DAT exam changes over time, and some publishers simply don’t update their preparation material to keep up with changes in the DAT syllabus. You want to make sure you don’t end up studying from out-dated material that’s not covered on the DAT exam.

For the list of topics covered on the DAT, go here.

Filed Under: canadian dat, dat exam, dental aptitude test Tagged With: canadian dat, dat aptitude test, dat exam

May 6, 2013 By Sales

How To Tackle The DAT PAT Cube Counting Section

Strategy:

A powerful strategy for this section is to count all the cubes with painted surfaces by making a tally chart on the test sheet.

Start counting from the top-front (the cube closest to you on the highest level) and work your way back on the same level. Once you are done with that level, go down a level below and repeat the process. This strategy will ensure you don’t miss any cubes, and you’ll also have answers for the next 2-3 questions, since a cube structure is used in more than one question.

Make sure you pay close attention to the hidden cubes as well!

datready_canadian_dat_pat_tip

Filed Under: canadian dat, dat cube counting, dat exam, dat pat Tagged With: canadian dat, dat cube counting, dat pat

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  • Tips from University of Toronto Dental Students
  • DAT Chemistry Tip: How To Solve Gibbs Free Energy Problems
  • How is the DAT scored?
  • Will You Ever Feel Ready For the DAT?
  • Join A Pre-Dental Student Club

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