Problem 15 - Chemistry An Atoms First Approach

Question

Explain the law of conservation of mass, the law of definite proportion, and the law of multiple proportions.

Step-by-Step Solution

Answer

The law of conservation of mass states that the total mass of products in a chemical reaction equals the total mass of reactants, meaning matter cannot be created or destroyed. The law of definite proportion states that a chemical compound always contains the same elements in the same ratio, regardless of sample size or source. The law of multiple proportions states that when two elements form different compounds, the mass ratios of the second element combined with a fixed mass of the first element will be simple whole numbers. For example, water always has a 2:1 hydrogen-to-oxygen ratio, and in carbon monoxide and carbon dioxide, the ratio of oxygen masses is 2:1.

Step 1: Law of Conservation of Mass

The law of conservation of mass states that matter cannot be created or destroyed in a chemical reaction. In other words, the total mass of the products formed in a chemical reaction must be equal to the total mass of the reactants used. This principle was first introduced by French chemist Antoine Lavoisier in the late 18th century. For example, if we have a chemical reaction between hydrogen gas (\(H_2\)) and oxygen gas (\(O_2\)) to form water (\(H_2O\)), the total mass of hydrogen and oxygen used in the reaction will be equal to the total mass of water formed.

Step 2: Law of Definite Proportion

The law of definite proportion, also known as the law of constant composition, states that a given chemical compound will always contain the same elements in the same ratio, regardless of the sample size or the source of the compound. This principle was first established by French chemist Joseph Proust. For example, water (\(H_2O\)) will always contain hydrogen and oxygen in a ratio of 2:1. This means that if we have a 100 gram sample of water, it will contain 88.8 grams of oxygen and 11.2 grams of hydrogen, maintaining the 2:1 ratio.

Step 3: Law of Multiple Proportions

The law of multiple proportions states that when two elements combine to form more than one compound, the ratios of the masses of the second element that combine with a fixed mass of the first element will be simple whole numbers. This principle was first established by English chemist John Dalton. For example, carbon and oxygen can form two different compounds: carbon monoxide (\(CO\)) and carbon dioxide (\(CO_2\)). In carbon monoxide, 12 grams of carbon (C) combine with 16 grams of oxygen (O). In carbon dioxide, the same 12 grams of carbon combine with 32 grams of oxygen (twice the amount of oxygen compared to carbon monoxide). The ratio of oxygen masses (O) between the two compounds is 32:16, which simplifies to the whole number ratio 2:1.