Laws of Chemical Reactions Quiz

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Questions and Answers

In a closed system, during a chemical reaction, what remains constant according to Lavoisier's Law?

The number of atoms

The number of moles

The sum of the masses of the reactants and products (correct)

The number of molecules

According to Proust's Law, what remains constant in a given chemical reaction?

The mass proportion of the substances reacting (correct)

The total number of molecules

The temperature of the system

The volume of reactants used

Which law describes the relationship between the masses of one element that combine with a fixed mass of another element in different compounds?

Law of Combining Volumes

Law of Multiple Proportions (correct)

Law of Definite Proportions

Law of Conservation of Mass

If 16g of oxygen reacts completely with a certain mass of carbon and 32g of oxygen reacts completely with a different mass of carbon, based on the Law of Multiple Proportions what is the ratio of these different masses of carbon?

1:2 Signup and view all the answers

In the reaction 2H₂ + O₂ → 2H₂O, what is the smallest whole number proportion?

2:1:2 Signup and view all the answers

The proportion in a chemical reaction can be interpreted in terms of which of the following?

Moles, mass, or volume Signup and view all the answers

What is the ratio of carbon to oxygen in carbon monoxide (CO)?

1:1 Signup and view all the answers

Which of the following statements is true regarding proportions in a chemical reaction?

The proportion is constant for any given reaction. Signup and view all the answers

In the formation of sulfur dioxide ($SO_2$) and sulfur trioxide ($SO_3$), if the mass of sulfur is kept constant, which ratio of oxygen masses is seen in these two compounds?

2:3 Signup and view all the answers

Which of the following reactions demonstrates Gay-Lussac's Law of Combining Volumes?

N₂(g) + 3H₂(g) -> 2NH₃(g) Signup and view all the answers

If one liter of nitrogen gas reacts completely with hydrogen gas according to Gay-Lussac's Law, how many liters of ammonia gas are produced?

2 liters Signup and view all the answers

Why does the mass appear to decrease when coal burns in an open system?

The carbon dioxide product is released into the atmosphere. Signup and view all the answers

Why does the mass appear to increase when steel wool burns in an open system?

The iron gains mass by reacting with oxygen to form iron oxide. Signup and view all the answers

What does the Law of Constant Proportions state about a chemical compound?

It always contains the same elements in the same proportions by mass. Signup and view all the answers

According to the Law of Multiple Proportions, if 1 gram of carbon combines with 2 grams of oxygen to form a certain compound, how much oxygen will combine with 1 gram of carbon to form a different compound with a ratio of 1:1?

1 gram Signup and view all the answers

If two samples of a substance have different mass ratios of their constituent elements, what can be said about the samples?

They likely represent different chemical compounds. Signup and view all the answers

Study Notes

Lei de Lavoisier (Conservação de Massa)

In a closed system, the sum of the masses of the reactants equals the sum of the masses of the products.
A closed system is a sealed container that does not allow the exchange of material with the outside environment.
Mass is conserved, but the number of moles, the number of molecules, and the number of atoms are not always conserved.

Lei de Proust (Proporções Fixas)

In a given chemical reaction, substances always react in the same mass proportion.
The proportion is usually expressed by small whole numbers.
The proportion is constant, regardless of the amount of reactants used.
Example: In the combustion reaction of carbon, the mass proportion between carbon and oxygen is always the same, regardless of the amount of carbon or oxygen used.

Lei de Dalton (Proporções Múltiplas)

When two chemical elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in the ratio of small whole numbers.
Example: Sulfur and oxygen can combine to form sulfur dioxide (SO2) or sulfur trioxide (SO3).
In the formation of SO2, 32 g of sulfur combines with 32 g of oxygen. To form SO3, 32 g of sulfur combines with 48 g of oxygen.
The ratio of the masses of oxygen that combine with the same mass of sulfur is 32:48, which simplifies to 2:3.

Proportions in Chemical Reactions

The ratio of reactants and products in a chemical reaction is called the proportion.
The proportion is constant for any given reaction, regardless of the amount of reactants used.
The smallest possible whole number ratio for a chemical reaction is called the smallest whole number proportion.
For example, in the reaction 2H₂ + O₂ → 2H₂O the smallest whole number proportion is 2:1:2.
This means that for every two moles of hydrogen (H₂), one mole of oxygen (O₂) is consumed to produce two moles of water (H₂O).
The proportion can be interpreted in terms of moles, mass, or volume.
The proportion is important because it allows us to predict the amount of products that will be formed from a given amount of reactants.

The Law of Multiple Proportions

The law of multiple proportions 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 element are in ratios of small whole numbers.
For example, carbon and oxygen can combine to form carbon dioxide (CO₂) and carbon monoxide (CO).
In CO₂, the ratio of carbon to oxygen is 1:2, while in CO, the ratio is 1:1.
This means that the mass of oxygen that combines with one gram of carbon in CO₂ is twice the mass of oxygen that combines with one gram of carbon in CO.

Gay-Lussac's Law of Combining Volumes

Gay-Lussac's Law of Combining Volumes states that when gases react, they do so in volumes that are in a simple whole number ratio.
This law is a direct consequence of Avogadro's Law, which states that equal volumes of gases at the same temperature and pressure contain the same number of molecules.
For example, in the reaction N₂ + 3H₂ -> 2NH₃, the ratio of volumes of nitrogen, hydrogen, and ammonia is 1:3:2.
This means that one liter of nitrogen gas will react with three liters of hydrogen gas to produce two liters of ammonia gas.
This law applies only to gases, not liquids or solids.

Key Takeaways

Proportions are crucial for understanding chemical reactions.
Proportions can be expressed in terms of moles, mass, or volume.
The Law of Multiple Proportions and Gay-Lussac's Law of Combining Volumes are essential laws governing chemical reactions.

Reactions in a Closed System

When carbon (coal) reacts with oxygen in combustion, it releases carbon dioxide (CO2) as a gas.
The CO2 gas escapes the system, causing a mass decrease on the side containing the burning coal. This leads to the scale tilting toward the burning coal.

Reactions in an Open System

When iron (steel wool) reacts with oxygen in combustion, it forms iron oxide (Fe2O3 or Fe3O4).
The mass of the iron oxide is greater than the initial mass of the iron, as oxygen is incorporated.
The scale tilts toward the side with the burning steel wool because the mass has increased.

Law of Constant Proportions

The law states that the same chemical compound always contains the same elements in the same proportion by mass.
This law is used to determine if samples consist of the same compound by comparing the ratios of the weights of different elements within them.
Variations in these ratios suggest different chemical compounds.

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Description

Test your knowledge on the fundamental laws of chemical reactions, including Lavoisier's Law of Mass Conservation, Proust's Law of Definite Proportions, and Dalton's Law of Multiple Proportions. Understand how these principles govern the behavior of substances in reactions.