4.3 Representation of Reactions

There are many ______ that are conveyed in a chemical reaction

Important pieces of information

Give examples of the following from the equation above: Coefficient, reactant, formula unit, physical state, products, subscript

The 2 in front of the HgO, 2HgO(s), HgO, (l), 2Hg(l) and O2(g), the 2 in O2

Chemists often create particulate models to:

Represent reactions on a molecular level

Why do chemists want to represent reactions on a molecular level?

To visualize the changes that take place as the atoms rearrange

Important parts of a representation of reactions on a molecular level:

Relative location, amount, species

How to determine relative location of particles when representing reactions on a molecular level?

By identifying phase or state of matter and context clues

Relative location of solid particles:

Close contact and in order

Why should solid particles be in close contact?

To maximize attractions and minimize repulsions

Relative location of liquid particles:

Close but showing some disorder

Disorder in terms of particles means:

Movement

Relative location of gas particles:

Spread out as far as possible

Why do gas particles spread out as far as possible?

To fill the space they are in

When representing aqueous solutions in diagram, we can sometimes only show:

Solute particles

In aqueous solution, ions should be:

Dissociated and include charge

How should solvent particles be oriented in representation diagrams of aqueous solution?

With the dipoles in the correct direction

Why should solvent particles be oriented with dipoles in the correct direction for representation diagrams of aqueous solution?

To maximize attractions and minimize repulsions with solvent and solute particles

If a substance that ionizes is placed in water, water molecules should be:

Oriented correctly

Movement of solid particles:

Vibrate on the spot

Movement of liquid particles:

Move around each other

Movement of gas particles:

Move quickly in all directions

What aspects of alloys should be represented in particle level diagrams?

Surface and interstices

How to represent precipitates in particle level diagrams?

Solid particles at the bottom once settled. A few may remain throughout.

Interfaces are where:

Two different substances meet

Example of interface:

Where water and air meet

How to represent substances when given the formula?

Use proper number of atoms for each element

How to represent substances when given a quantity?

Use relative amounts of atoms

Examples of quantities to show you how to represent substances:

mol, concentration, coefficient in equation, etc

When drawing particle level diagrams, you should observe the:

Law of conservation of mass

How to show observance of the law of conservation of mass when drawing particle level diagrams?

Keep the same number of each type of atom present before and after the reaction, just rearrange them appropriately

How to identify atoms/ions of different elements in particle representation diagrams?

By using distinct shapes, symbols, colors, or shades

What should you do to charges in particle representation diagrams?

Show them and align them appropriately

What should you do for polar molecules if there are intermolecular forces (IMF) in particle representation diagrams?

Use partial charges on them

Make sure the charges and dipole moments:

Align properly

Why should you make sure that the charges and dipole moments align properly?

To maximize attractions and minimize repulsions

Size of atoms of the same element:

Same throughout

How to determine relative size of atoms of different elements?

By following atomic/ionic trends on periodic table