## Basic Concept

Avogadro's Law states that for a gas at constant temperature and pressure the volume is directly proportional to the number of moles of gas.

V1 / n1 = constant

After the change involume and mole number,

V2 / n2 = constant

Combine the two:

V1 / n1 = V2 / n2

When any three of the four quantities in the equation are known, the fourth can be calculated. For example, if n1, V1 and V2 are known, the n2 can be solved by the following equation:

n2  = V2 x (n1/V1)

#### Pressure

The force exerted per unit area of surface, typical pressure units are ATM, mmHg and kPa.

#### Volume

The measurement of space taken by a substance, it is length cubed, typical units are L, mL and m3.

#### Temperature

A measure of the average kinetic energy of the particles in a sample of matter, expressed in terms of units or degrees designated on a standard scale. Typical units are K, F and C.

#### Density

The mass of the object divided by its volume. Typical units are g/mL and kg/m3.

#### Formula Weight / Molecular Weight (MW)

The formula weight of a compound is the sum of all the atomic weights of the elements present in the formula of the compound. Some text also refers it to formula mass. Typical unit is g/mol.

#### Mass and Mole

Mass is the amount of a substance in grams, also called weight.

#### Gas Constant (R)

The constant that appears in the ideal gas equation (PV=nRT). It is usually expressed as 0.08206 L x atm/K x mol or 8.314 J/K x mol.

#### Molality

The number of moles of solute dissolved in one kilogram of solvent.

#### Molarity

The number of moles of solute in one liter of solution.

## Feature Overview

With four quantities in V1 / n1 = V2 / n2  equation, given any three, the forth one can be calculated based on the Avogadro's Law.

In addition to the problem solving module, the "Show Work" is also displayed along with the solution to illustrate the step-by-step guide in how your problem has been solved.

## User Instructions

This is one step process, enter the known data and press Calculate to output the unknowns.

1. Select Avogadro's Law link from the front page or Avogadro tab from the Gases module. The Input and Output screen appears.

2. In the Input area, enter the three known quantities with a proper significant figure. Select the units associated with the input.

3. Click Calculate to output the answer.

4. The Show Work area on the right shows you step-by-step how your problem has been solved.

To start a new problem, click Reset. All Input fields will be cleared. Follow Step 1-3 again.