Unit 7 - Chemical Reactions Review
In science, a chemical reaction is a process that leads to the transformation of one set of chemical substances to another. This typically involves the changing of electron positions in the manipulation of chemical bonds between atoms.
Questions and Answers
- 1.
What type of reaction produces a precipitate?
- A.
Synthesis
- B.
Single displacement
- C.
Double displacement
- D.
Decomposition
Correct Answer
C. Double displacementExplanation
Double displacement reactions produce a precipitate. In a double displacement reaction, the positive ions of two compounds switch places, forming two new compounds. If one of the products is insoluble in water, it will form a solid precipitate. This occurs because the positive and negative ions of the reactants combine to form an insoluble compound, which then separates from the solution as a solid.Rate this question:
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- 2.
____ is a way to describe a chemical reaction using chemical formulas and symbols.
- A.
Synthesis
- B.
A physical law
- C.
The law of conservation of matter
- D.
A chemical equation
Correct Answer
D. A chemical equationExplanation
A chemical equation is a way to describe a chemical reaction using chemical formulas and symbols. It represents the reactants and products involved in the reaction and provides information about the stoichiometry of the reaction, such as the number of molecules or moles of each substance. It allows scientists to understand and communicate the specific chemical changes that occur during a reaction. The other options, synthesis, a physical law, and the law of conservation of matter, do not accurately describe the concept of using chemical formulas and symbols to represent a chemical reaction.Rate this question:
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- 3.
An insoluble compound that comes out of solution during a double displacement reaction is called a _____.
- A.
Reactant
- B.
Solvent
- C.
Precipitate
- D.
Catalyst
Correct Answer
C. PrecipitateExplanation
During a double displacement reaction, two compounds exchange ions to form two new compounds. Sometimes, one of the products formed is insoluble in the reaction mixture and separates out as a solid. This solid is called a precipitate. Therefore, the correct answer is precipitate.Rate this question:
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- 4.
What does it mean for a chemical equation to be balanced?
- A.
The number of reactants is equal to the number of products.
- B.
The reactants and products are written with the same coefficients.
- C.
The same number of atoms of each element is on both sides of the equation.
- D.
The solid products weight the same as the reactants.
Correct Answer
C. The same number of atoms of each element is on both sides of the equation.Explanation
A balanced chemical equation means that the number of atoms of each element is the same on both sides of the equation. This is important because it ensures that the law of conservation of mass is obeyed. In a balanced equation, the total mass of the reactants is equal to the total mass of the products, indicating that no atoms are created or destroyed during the reaction. By adjusting the coefficients in the equation, we can achieve this balance and accurately represent the reaction.Rate this question:
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- 5.
In chemical equations, ______ represents the number of units of each substance.
- A.
Precipitates
- B.
Products
- C.
Reactants
- D.
Coefficients
Correct Answer
D. CoefficientsExplanation
Coefficients in chemical equations represent the number of units of each substance. They are used to balance the equation by ensuring that the number of atoms on both sides of the equation is equal. Coefficients indicate the ratio in which substances react or are produced in a chemical reaction.Rate this question:
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- 6.
The chemical formula for a compound tells _____.
- A.
How stable the compound is
- B.
What type of chemical bond it forms
- C.
How electrons are arranged
- D.
What elements it contains
Correct Answer
D. What elements it containsExplanation
The chemical formula for a compound tells what elements it contains. The chemical formula represents the types and number of atoms of each element present in the compound. It provides a concise and standardized way to represent the composition of a compound. By knowing the chemical formula, one can determine the elements that make up the compound and their respective ratios.Rate this question:
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- 7.
If electric current passes through water and initiates a decomposition reaction, what are the expected products?
- A.
Oxygen and water
- B.
Hydrogen and oxygen
- C.
Hydrogen peroxide
- D.
Hydrogen oxide
Correct Answer
B. Hydrogen and oxygenExplanation
When an electric current passes through water, a process known as electrolysis occurs. During electrolysis, water molecules are broken down into their constituent elements. The positive electrode (anode) attracts negatively charged hydroxide ions (OH-) and causes the oxidation of water molecules, resulting in the release of oxygen gas (O2). At the same time, the negative electrode (cathode) attracts positively charged hydrogen ions (H+) and causes the reduction of water molecules, leading to the formation of hydrogen gas (H2). Therefore, the expected products of the decomposition reaction are hydrogen and oxygen.Rate this question:
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- 8.
When iron combines with oxygen and water in the air to form rust, what substance in the reaction is the product?
- A.
Iron
- B.
Rust
- C.
Water
- D.
Oxygen
Correct Answer
B. RustExplanation
When iron combines with oxygen and water in the air to form rust, the substance that is produced in the reaction is rust. Rust is a reddish-brown compound that forms on the surface of iron when it reacts with oxygen and water. It is a common form of corrosion and is composed mainly of hydrated iron(III) oxide.Rate this question:
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- 9.
As a result of the experiments of Lavoisier, you know that in a chemical reaction the masses of the products _____.
- A.
Is less than the mass of the reactants
- B.
Always equals the mass of the reactants
- C.
Cannot be predicted based on the mass of the reactants
- D.
Is twice as great as the mass of the reactants
Correct Answer
B. Always equals the mass of the reactantsExplanation
The correct answer is "always equals the mass of the reactants." This is based on the law of conservation of mass, which states that mass is neither created nor destroyed in a chemical reaction. Therefore, the total mass of the products must be equal to the total mass of the reactants.Rate this question:
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- 10.
New substances produced by a chemical reaction are ____.
- A.
Products
- B.
Resultants
- C.
Reactants
- D.
Coefficients
Correct Answer
A. ProductsExplanation
In a chemical reaction, new substances are formed as a result of the reaction. These new substances are called products. Reactants are the substances that undergo the reaction, while coefficients are used to balance the equation representing the reaction. Resultants is not a term commonly used in chemistry to describe the new substances formed in a chemical reaction.Rate this question:
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- 11.
In a ______ reaction, two or more substances combine to form another substance.
- A.
Single displacement
- B.
Double displacement
- C.
Decomposition
- D.
Synthesis
Correct Answer
D. SynthesisExplanation
In a synthesis reaction, two or more substances combine to form another substance. This type of reaction is characterized by the formation of a new compound from simpler reactants. It involves the combination of atoms or molecules to create a more complex product.Rate this question:
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- 12.
A change in which one or more substances are converted into new substances is a _____.
- A.
Nuclear reaction
- B.
Chemical reaction
- C.
Chemical fusion
- D.
Physical change
Correct Answer
B. Chemical reactionExplanation
A change in which one or more substances are converted into new substances is known as a chemical reaction. In a chemical reaction, the bonds between atoms in the reactants are broken and new bonds are formed to create different substances. This process involves the rearrangement of atoms and the release or absorption of energy. Unlike physical changes, which only affect the physical properties of a substance, chemical reactions result in the formation of entirely new substances with different chemical properties.Rate this question:
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- 13.
A(n) _____ is a substance that speeds up a chemical reaction without being permanently changed itself.
- A.
Catalyst
- B.
Inhibitor
- C.
Exotherm
- D.
Endotherm
Correct Answer
A. CatalystExplanation
A catalyst is a substance that speeds up a chemical reaction without being permanently changed itself. It works by lowering the activation energy required for the reaction to occur, allowing it to happen more quickly. This is achieved by providing an alternative reaction pathway with a lower energy barrier. The catalyst is not consumed in the reaction and can be used repeatedly.Rate this question:
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- 14.
Why is oxygen written with a subscript 2?
- A.
It usually exists as a diatomic molecule.
- B.
Its mass is twice as great as the reactants'.
- C.
There are two times as many oxygen atoms as reactant atoms.
- D.
Its mass increases by two times as a result of the reaction.
Correct Answer
A. It usually exists as a diatomic molecule.Explanation
Oxygen is written with a subscript 2 because it usually exists as a diatomic molecule. This means that oxygen atoms typically bond together in pairs, forming O2 molecules. This is the most stable and common form of oxygen found in nature.Rate this question:
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- 15.
The law of conservation of mass states that _____.
- A.
In a chemical reaction, matter is not created or destroyed, but is conserved.
- B.
Matter can be created and destroyed but does not change forms.
- C.
In a chemical reaction, efforts should be made to preserve rare elements without changing them.
- D.
In a chemical reaction, the final mass of the products is always greater than the starting mass of the reactants.
Correct Answer
A. In a chemical reaction, matter is not created or destroyed, but is conserved.Explanation
The law of conservation of mass states that matter is not created or destroyed, but is conserved. This means that in a chemical reaction, the total mass of the reactants will be equal to the total mass of the products. The atoms in the reactants may rearrange to form different molecules in the products, but the total number of atoms remains the same. This principle is fundamental in chemistry and is used to balance chemical equations and analyze reactions.Rate this question:
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- 16.
Which of the following is a chemical reaction?
- A.
Water freezing into ice
- B.
Water evaporating from salt water leaving salt crystals
- C.
Dew forming on grass
- D.
Rust forming on a car body
Correct Answer
D. Rust forming on a car bodyExplanation
Rust forming on a car body is a chemical reaction because it involves a chemical change. Rust is formed when iron reacts with oxygen in the presence of water or moisture, resulting in the formation of iron oxide. This process is known as oxidation and is a chemical reaction. In contrast, the other options mentioned are physical changes rather than chemical reactions.Rate this question:
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- 17.
Some elements usually exist in combinations of two atoms. These combinations are called ______.
- A.
Diatomic molecules
- B.
Coefficients
- C.
Ions
- D.
Isotopes
Correct Answer
A. Diatomic moleculesExplanation
Diatomic molecules refer to combinations of two atoms that are usually found together. These molecules can be made up of the same element or different elements. Examples of diatomic molecules include oxygen (O2), nitrogen (N2), and hydrogen (H2). These molecules are stable and have specific properties that differ from their individual atoms.Rate this question:
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- 18.
Identify the following as either endothermic or exothermic. The temperature of the beaker holding the reacting substances is increased.
- A.
Endothermic
- B.
Exothermic
Correct Answer
B. ExothermicExplanation
When the temperature of the beaker holding the reacting substances is increased, it indicates that heat is being released from the reaction. This release of heat is characteristic of an exothermic reaction, where energy is transferred from the system (reacting substances) to the surroundings (beaker). Therefore, the correct answer is exothermic.Rate this question:
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- 19.
Identify the following as either endothermic or exothermic. The temperature of the beaker holding the reacting substances is decreased.
- A.
Endothermic
- B.
Exothermic
Correct Answer
A. EndothermicExplanation
When the temperature of the beaker holding the reacting substances is decreased, it indicates that heat is being absorbed from the surroundings. This suggests that the reaction is endothermic, as it requires an input of energy (in the form of heat) to proceed.Rate this question:
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- 20.
Identify the following as either endothermic or exothermic. Frost formed on the outside of the beaker holding the reacting substances.
- A.
Endothermic
- B.
Exothermic
Correct Answer
A. EndothermicExplanation
The formation of frost on the outside of the beaker suggests that heat is being absorbed from the surroundings, causing a decrease in temperature. This indicates an endothermic reaction, as it requires an input of energy in the form of heat to occur.Rate this question:
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Mar 22, 2023Quiz Edited by
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Jan 14, 2013Quiz Created by
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