Laws of Chemical Combination: 56 MCQs with answers

Law of Conservation of Mass

The Law of Conservation of Mass, proposed by Antoine Lavoisier, states that mass is neither created nor destroyed in a chemical reaction.

Law of Definite Proportions

The Law of Definite Proportions (Proust's Law) states that a given compound always has the same elements in the same proportion by mass.

John Dalton

John Dalton proposed the Law of Multiple Proportions in 1803.

Avogadro's Law

Avogadro's Law states that equal volumes of all gases at the same temperature and pressure contain equal numbers of molecules, leading to the molar volume of $22.4\,\text{L}$ at STP.

Law of Conservation of Mass

The total mass of products ($5.6 + 4.4 = 10.0\,\text{g}$) equals the mass of the reactant, illustrating the Law of Conservation of Mass.

True

The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction; it was proposed by Antoine Lavoisier.

Mass is neither created nor destroyed in chemical reactions.

The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction, meaning the total mass of reactants equals the total mass of products.

Law of Definite Proportions

The Law of Definite Proportions states that a given compound always contains the same proportion of elements by mass, regardless of its source.

John Dalton

The Law of Multiple Proportions was proposed by John Dalton in 1803, stating that when two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in a ratio of small whole numbers.

Gases react in simple volume ratios at the same temperature and pressure.

Gay-Lussac's Law states that when gases combine or are produced in a chemical reaction, they do so in a simple ratio by volume, provided all gases are at the same temperature and pressure.

Avogadro's Law

Avogadro's Law states that equal volumes of all gases at the same temperature and pressure contain equal numbers of molecules, which is fundamental to understanding gas behavior.

The same elements can form more than one compound with different mass ratios.

The Law of Multiple Proportions describes how the same elements can combine to form more than one compound, with the masses of one element combining with a fixed mass of the other in small whole number ratios.

Water always contains hydrogen and oxygen in a $1:8$ mass ratio.

The classic example illustrating the Law of Definite Proportions is that water always contains hydrogen and oxygen in a $1:8$ mass ratio, regardless of its source.

Gay-Lussac's Law

Gay-Lussac's Law applies only to gases, stating that they react in simple volume ratios when at the same temperature and pressure.

Equal volumes of gases have equal molecules at the same temperature and pressure.

Avogadro's Law states that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules, linking volume and the number of particles.

Law of Conservation of Mass

The Law of Conservation of Mass is crucial for balancing chemical equations as it ensures that the mass of reactants equals the mass of products in a reaction.

Mass is neither created nor destroyed in a chemical reaction.

The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction, meaning the total mass of reactants equals the total mass of products.

Law of Definite Proportions

The Law of Definite Proportions states that a given compound always contains the same proportion of elements by mass, regardless of its source.

John Dalton

The Law of Multiple Proportions was proposed by John Dalton in 1803, describing how two elements can form multiple compounds.

Gases react in simple ratios by volume at the same temperature and pressure.

Gay-Lussac's Law of Gaseous Volumes states that gases react in simple ratios by volume, provided they are at the same temperature and pressure.

Mass ratios of one element in different compounds formed by the same two elements.

The Law of Multiple Proportions focuses on the mass ratios of one element that combine with a fixed mass of another element in different compounds.

Avogadro's Law

Avogadro's Law states that equal volumes of all gases at the same temperature and pressure contain equal numbers of molecules.

Water always contains hydrogen and oxygen in a $1:8$ mass ratio.

The Law of Definite Proportions is illustrated by water, which always has a mass ratio of hydrogen to oxygen of $1:8$.

Gay-Lussac's Law of Gaseous Volumes

Gay-Lussac's Law of Gaseous Volumes explains that gases react in simple ratios by volume when at the same temperature and pressure.

The total mass of reactants equals the total mass of products.

The Law of Conservation of Mass implies that in a chemical reaction, the total mass of reactants equals the total mass of products.

It states that a compound has a fixed composition by mass.

The Law of Definite Proportions is significant because it states that a compound always has a fixed composition by mass, regardless of its source.

$1:2$

In CO, 12 g C combines with 16 g O; in $CO_2$, 12 g C combines with 32 g O. The ratio of oxygen masses is $16:32 = 1:2$.

Gay-Lussac's Law of Gaseous Volumes

Gay-Lussac's Law of Gaseous Volumes applies only to gases, as it deals with volume ratios of gaseous reactants and products.

Law of Multiple Proportions

Two different compounds of the same elements show a simple whole-number ratio of oxygen masses ($16:32 = 1:2$) for fixed nitrogen mass, illustrating the Law of Multiple Proportions.

Law of Multiple Proportions

The Law of Multiple Proportions helps determine molecular formulas from empirical formulas because it deals with different compounds of the same elements.

Both A and R are true, and R is the correct explanation of A.

The Law of Conservation of Mass fails in nuclear reactions because mass is converted to energy via $E = mc^2$, so R correctly explains A.

Law of Partial Pressures

The Law of Partial Pressures is a gas law proposed by Dalton, not one of the five Laws of Chemical Combination.

1:2, Law of Multiple Proportions

The mass ratio of oxygen in the two compounds is $16:32 = 1:2$, illustrating the Law of Multiple Proportions, which states that when two elements form multiple compounds, the masses of one element that combine with a fixed mass of the other are in a ratio of small whole numbers.

Law of Definite Proportions

This exemplifies the Law of Definite Proportions, which states that a given compound always contains the same proportion of elements by mass, regardless of its source.

Law of Conservation of Mass

This demonstrates the Law of Conservation of Mass, which states that mass is neither created nor destroyed in a chemical reaction, as the total mass of reactants equals the total mass of products.

Gay-Lussac's Law of Gaseous Volumes

This illustrates Gay-Lussac's Law of Gaseous Volumes, which states that gases react in simple ratios by volume when at the same temperature and pressure.

N, according to Avogadro's Law

According to Avogadro's Law, equal volumes of gases at the same temperature and pressure contain equal numbers of molecules, so 1 L of $O_2$ also contains $N$ molecules.

Law of Multiple Proportions

This is the Law of Multiple Proportions, which states that the masses of one element that combine with a fixed mass of another element are in ratios of small whole numbers.

Law of Conservation of Mass

This supports the Law of Conservation of Mass, which states that mass is conserved in a chemical reaction, meaning the total mass of reactants equals the total mass of products.

Law of Multiple Proportions

This illustrates the Law of Multiple Proportions, as it shows how the masses of one element (B) that combine with a fixed mass of another element (A) are in a ratio of small whole numbers.

Definite Proportions applies to one compound, Multiple Proportions to multiple compounds

The Law of Definite Proportions applies to a single compound, stating it has a fixed composition, while the Law of Multiple Proportions applies to two or more compounds formed from the same elements, focusing on their mass ratios.

The gases react in a simple ratio by volume

This indicates that the gases react in a simple ratio by volume, as stated by Gay-Lussac's Law of Gaseous Volumes, which applies when all gases are at the same temperature and pressure.

$1:2$

In $N_2O$, 28 g N combines with 16 g O; in NO, 28 g N combines with 32 g O. The ratio of oxygen masses is $16:32 = 1:2$.

Law of Multiple Proportions

Two different compounds of H and O show a simple whole-number ratio of oxygen masses ($8:16 = 1:2$) for fixed hydrogen mass, illustrating the Law of Multiple Proportions.

$N$

According to Avogadro's Law, equal volumes of all gases at the same temperature and pressure contain equal numbers of molecules. So 1 L of $O_2$ also contains $N$ molecules.

Law of Definite Proportions

The mass ratio of elements in a single compound ($CO_2$) is fixed and illustrates the Law of Definite Proportions.

1:2, illustrating the Law of Multiple Proportions

The correct option is 1:2, illustrating the Law of Multiple Proportions. This law states that when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other are in a ratio of small whole numbers. Here, 16 g of O in the first compound and 32 g of O in the…

1:1.5; Law of Multiple Proportions

The masses of oxygen in the two compounds are in a ratio of $32:48$, which simplifies to $2:3$. This demonstrates the Law of Multiple Proportions, as it shows how two different compounds of the same elements can have mass ratios of one element that combine with a fixed mass of the other in small whole numbers.

1:3; Law of Multiple Proportions

The mass ratios of oxygen in the two nitrogen oxides are $16:48$, which simplifies to $1:3$. This illustrates the Law of Multiple Proportions, as it shows how different compounds formed from the same elements can have mass ratios of one element that combine with a fixed mass of the other in simple whole numbers.

Mass is conserved; the reaction supports the law

The total mass of reactants (10 g + 15 g = 25 g) does not equal the total mass of products (24 g), indicating a discrepancy. However, if we assume that the reaction was not complete or there was measurement error, the Law of Conservation of Mass states that mass must be conserved in a closed system.

Mass is not conserved; the law is violated

In the first reaction, the total mass of products (20 g + 5 g = 25 g) does not equal the total mass of reactants (25 g), indicating that mass is conserved. However, in the second reaction, the mass of products is greater than the reactants, violating the Law of Conservation of Mass.

1:4; Law of Multiple Proportions

The mass ratio of oxygen in the two compounds is $8:16$, which simplifies to $1:2$. This illustrates the Law of Multiple Proportions, as it shows how the same element (carbon) combines with different masses of another element (oxygen) in small whole-number ratios.

Gases react in simple volume ratios

This reaction demonstrates Gay-Lussac's Law of Gaseous Volumes, which states that gases react in simple ratios by volume, provided all gases are at the same temperature and pressure.

N; Avogadro's Law

According to Avogadro's Law, equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. Therefore, if 1 L of methane contains $N$ molecules, 1 L of ethane will also contain $N$ molecules.

1:1.5; Law of Multiple Proportions

The mass ratios of oxygen in the two compounds are $6:12$, which simplifies to $1:2$. This illustrates the Law of Multiple Proportions, as it shows how two different compounds formed from the same elements can have mass ratios of one element that combine with a fixed mass of the other in simple whole numbers.

Mass is conserved; error in measurement

The discrepancy suggests a measurement error, as the Law of Conservation of Mass states that mass must be conserved in a closed system. Therefore, the mass of reactants should equal the mass of products.