1. What is Average Molecular Weight?

The average molecular weight (MW_avg) is the weighted mean of the molecular weights of all components in a mixture, where the weights are the mole fractions of each component. It's commonly used in polymer chemistry and gas mixtures.

2. How Does the Calculator Work?

The calculator uses the average molecular weight formula:

Where:

• \( MW_{avg} \) — Average molecular weight (g/mol)
• \( MW_i \) — Molecular weight of component i (g/mol)
• \( fraction_i \) — Fraction of component i (unitless, sum must equal 1)

Explanation: The equation calculates the weighted average where each component's molecular weight is multiplied by its fraction in the mixture, then summed.

3. Importance of Average MW Calculation

Details: Average molecular weight is crucial for understanding mixture properties, calculating reaction yields, determining gas densities, and characterizing polymer distributions.

4. Using the Calculator

Tips:

• Enter molecular weights in g/mol
• Fractions must be between 0 and 1
• The sum of all fractions must equal exactly 1
• Use the Add/Remove buttons to adjust the number of components

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between number-average and weight-average MW?
A: Number-average (calculated here) weights each molecule equally, while weight-average weights larger molecules more heavily.

Q2: How do I convert mass fraction to mole fraction?
A: First convert mass to moles for each component using MW, then calculate mole fractions from the total moles.

Q3: What if my fractions don't sum to 1?
A: The calculator will show an error. Normalize your fractions by dividing each by the total.

Q4: Can I use this for polymer mixtures?
A: Yes, but for polymers you may need additional calculations for polydispersity.

Q5: How precise should my fractions be?
A: Use at least 3 decimal places for accurate results in most applications.