Problem 68 - Chemistry: Atoms First

Question

A very good 197-lb weight lifter lifted 192 kg in a move called the clean and jerk. What was the mass of the weight lifted in pounds?

Step-by-Step Solution

Answer

The mass of the weight lifted was approximately 423.3 pounds.

Step 1: Convert kilograms to pounds

To convert the mass of the weight lifted from kilograms to pounds, use the conversion factor that 1 kilogram is approximately equal to 2.20462 pounds.

Step 2: Calculate the mass in pounds

Multiply the mass of the weight lifted in kilograms by the conversion factor to find the mass in pounds. That is, multiply 192 kg by 2.20462 pounds/kg.

Step 3: Determine the final answer

Perform the multiplication to get the mass in pounds. If the multiplication is done correctly, it will provide the mass of the weight lifted in pounds. Calculation: 192 kg * 2.20462 pounds/kg = 423.2864 pounds

Key Concepts

Mass Unit Conversion

When studying chemistry or physics, you'll often find yourself needing to convert units of mass from one system to another. The concept of mass unit conversion is fundamental as various fields, including science, engineering, and trade, use different units.
A common task might be converting kilograms, the international standard of mass, to pounds, commonly used in the United States. Understanding how to convert between units allows you to follow recipes, understand weight restrictions, and grasp scientific data regardless of the units presented.
Knowing the equivalence between kilograms and pounds is crucial for conversions: 1 kilogram is approximately equal to 2.20462 pounds. To convert a mass from kilograms to pounds, you multiply the amount in kilograms by this conversion factor.

Kilograms to Pounds

In practical terms, converting kilograms to pounds is a simple multiplication task using the conversion factor. For example, let's say you're at the gym and the weight plate is marked in kilograms, but you wish to know how much that is in pounds. To convert a weight from kilograms to pounds, you take the weight in kilograms and multiply it by approximately 2.20462, since there are roughly 2.20462 pounds in a kilogram.
Calculators or smartphone conversion apps can provide a quick conversion, but it's also useful to know how to do this manually, especially in a testing situation. A rounded conversion factor of 2.2 is often used for easier calculations, but for precise scientific work, the exact factor of 2.20462 is preferred.

Conversion Factors

Conversion factors are ratios that allow you to convert a quantity expressed in one set of units to an equivalent quantity in another set of units. They are the backbone of unit conversion in chemistry and other sciences. A conversion factor is a way of expressing the same quantity in two different units, such as the 1 kg to 2.20462 lbs factor previously mentioned.
Using conversion factors requires understanding the relationship between the units in question. For instance, if you wanted to convert miles to kilometers, you would need to know the appropriate conversion factor. It's also essential to ensure that the factor is used in the correct direction to prevent inverting the conversion.

Stoichiometry

Stoichiometry is a section of chemistry that involves calculating the amounts of reactants and products in chemical reactions. In a broader sense, it can also apply to the calculations involving the conversion of physical quantities in a systematic way, like our weight lifting example.
While stoichiometry commonly deals with mole-to-mole conversions, it can also entertain different units, such as converting the mass of a substance to an equivalent mass in another unit system using conversion factors. Thus, understanding stoichiometry isn't only for chemical equations but is also valuable for everyday practical conversions. It emphasizes the quantitative relationships and the conservation of mass, where accurate and precise conversions are vital.