Effect of Temperature on GIbbs Free Energy

Imagine a reaction in which you decompose liquid water to produce oxygen gas and hydrogen gas:

H₂O_(l) → H_2(g) + ½O_2(g)

The reaction is endothermic, ΔH > 0, and the change in entropy is also positive, ΔS > 0
At room temperature and pressure this reaction is not spontaneous ( ΔG > 0).
But could I heat, or cool, the reaction sufficiently to make the reaction spontaneous?
Can I turn a nonspontaneous reaction into a spontaneous reaction by changing the temperature?
Want to know?
Go to https://www.ausetute.com.au/gibbstemp.html

AUS-e-TUTE Members can access the tutorial, game, test and exam by logging-in to the Members Only area of the website.

Gibbs Free Energy Calculations

For a chemical system, either a chemical reaction or a physical change, at a constant temperature and pressure we define a function called the Gibbs Free Energy (G) so that we can determine whether the system will be spontaneous or non-spontaneous:

• spontaneous if ΔG < 0 (ΔG is negative)
• non-spontaneous if ΔG > 0 (ΔG is positive)

In this new tutorial we will calculate the change in Gibbs free energy of a reaction at constant temperature and pressure (ΔG) using:

• standard absolute entropy of each reactant and product (S°)
• standard enthalpy of formation of each reactant and product (ΔH_ƒ°)

For a chemical system under standard conditions, we can calculate the change in standard Gibbs free energy using the equation shown below:

ΔG° = ΔH° - TΔS°

AUS-e-TUTE members can access the new Gibbs free energy calculations tutorial, game, test and exam when they log-in (Go to Physical Chemistry Heading, then "Thermodynamics").

If you are not an AUS-e-TUTE member, there is a "free-to-view" Gibbs free energy calculations tutorial currently available for evaluation purposes at https://www.ausetute.com.au/gibbscalc.html

Calculating Entropy Changes

If you stick some clean reactive metal, like magnesium, into an aqueous solution of hydrochloric acid... Hey presto! Bubbles of hydrogen gas! This gas production is a dead giveaway that the entropy of the system has increased.
But what if all the reactants and products are soluble in water and the entire chemical process occurs in aqueous solution. Has the entropy of the system increased or decreased?
Thankfully, chemists have a tool they can use to make quantitative predictions about the changes in entropy of a chemical system (ΔS). This tool is called the Standard Absolute Entropy (S°), and we have just added a new tutorial, game, test and exam to help you understand what this is and how it can be used.
AUS-e-TUTE Members should log-in to access the new resources under the heading "Thermodynamics".
If you are not already an AUS-e-TUTE there is a "free-to-view" tutorial currently available at https://www.ausetute.com.au/entropychange.html

Bleach

Lurking in my laundry cupboard is an opaque, plastic bottle containing bleach. I use it to whiten white clothes when they start to look a bit grey, but I also use it to clean blood stains, to remove mildew from walls and ceilings, and to remove the mould from bathroom tiles. The active ingredient in laundry bleach is sodium hypochlorite, NaOCl, and you will find a similar substance present in the "liquid chlorine" you add to swimming pools as a disinfectant.

Sodium hypochlorite is a very useful chemical, but it can also be dangerous if used incorrectly. 

The September 2018 issue of AUS-e-NEWS, AUS-e-TUTE's free quarterly newsletter for chemistry students and teachers, looks at the chemistry of bleach.

If you would like to subscribe to AUS-e-NEWS please go to https://www.ausetute.com.au/ausenews.html

Name and Formula of Inorganic Acids

There are systematic ways to name inorganic acids, however, for many acids no-one uses these systematic names because the "acid name" for these particular acids has been in use for a very long time. So, IUPAC recognises the "acid name" for a number of acids.
AUS-e-TUTE has just added a new tutorial, game, test, quiz and worksheet wizard, as well as a card game, to help you give the name and molecular formula of these acids. AUS-e-TUTE members should log-in to use these new resources.

If you are not an AUS-e-TUTE member, there is a "free-to-view" tutorial currently available at
https://www.ausetute.com.au/acidnames.html

Don't forgot to download our free "Inorganic Acid Names Card Games" when you visit!
(includes instructions for 3 games and a set of game cards).

Name and Formula of Inorganic Molecules

Non-metallic elements combine to produce covalent compounds, that is, molecules in which the atoms are held together by covalent bonds.
But do you know how to name these molecules using IUPAC recommendations?
Can you write the formula for these molecules using IUPAC recommendations?

AUS-e-TUTE has just added new resources on these topics.
AUS-e-TUTE members should log-in to access the tutorials, games, tests, exams, drills.
AUS-e-TUTE class and school group members also have access to the online quizzes.
Teachers registered with a class or school group can also access the worksheet wizards (instant worksheets, with answers, at the click of button!).

If you are not an AUS-e-TUTE member, there are two "free-to-view" tutorials currently available:

Naming Binary Inorganic Non-metallic Compounds

Molecular Formula of Binary Inorganic Non-metallic Compounds

Explosive Medicine

You’ve probably heard of Alfred Nobel, the inventor of dynamite and gelignite. The commercialisation of these explosives enabled him to accumulate great wealth during his lifetime which, by the terms of his will signed in 1895, was used to establish the Nobel Prize. In later life he was prescribed Trinitrin, a medication used to relieve a heart condition known as angina.

What do dynamite, gelignite and Trinitrin all have in common?

They all contain nitroglycerin!

This is not a story about the life of Alfred Nobel.

It is a story about the fascinating chemistry of nitroglycerin…

Read more in the June 2018 issue of AUS-e-NEWS, AUS-e-TUTE's free quarterly newsletter for chemistry students and teachers.

Subscribe to AUS-e-NEWS at https://www.ausetute.com.au/ausenews.html