Ch5 Chemical Reactions
Chapter 5 Unit Test
Chemical Reactions
Questions and Answers
- 1.
Which of the following does not indicate a chemical change has occurred?
- A.
Color change
- B.
Formation of a precipitate
- C.
Change in surface are
- D.
Gas production
Correct Answer
C. Change in surface areExplanation
A change in surface area does not indicate a chemical change because it is a physical change. Physical changes involve alterations in the physical properties of a substance, such as size, shape, or state, without forming new substances. In contrast, chemical changes involve the formation of new substances with different chemical properties. The other options listed, including color change, formation of a precipitate, and gas production, are all indicators of a chemical change because they involve the formation of new substances.Rate this question:
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- 2.
When balancing equation, you are only allowed to change the _________ in the chemical equation.
- A.
Products
- B.
Reactants
- C.
Coefficients
- D.
Subscripts
Correct Answer
C. CoefficientsExplanation
When balancing a chemical equation, the only thing that can be changed are the coefficients. Coefficients are the numbers that appear in front of the reactants and products, indicating the number of molecules or moles involved in the reaction. By adjusting the coefficients, the equation can be balanced by ensuring that the number of atoms of each element is the same on both sides of the equation. Changing the subscripts would alter the actual chemical formula, and changing the reactants or products would result in a different chemical reaction.Rate this question:
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- 3.
Which of the following equation is chemically balanced? a. 2H2O à H2 + O2 b. Zn + 2HCl à ZnCl2 + H2 c. C2H5OH + 2O2 à 3CO2 + 3H2O d. NaOH + 2HCl à NaCl + H2O
- A.
A
- B.
B
- C.
C
- D.
D
Correct Answer
B. BExplanation
Option b is the correct answer because the equation Zn + 2HCl à ZnCl2 + H2 is balanced. The number of atoms on both sides of the equation is equal, and the charges are also balanced.Rate this question:
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- 4.
The burning of wood produces loss of heat and is an example of a(n) ________ reaction.
- A.
Exothermic
- B.
Endothermic
- C.
Nuclear
- D.
Terminal
Correct Answer
A. ExothermicExplanation
The burning of wood produces loss of heat, which indicates that it is releasing energy to the surroundings. This is characteristic of an exothermic reaction, where energy is being released in the form of heat.Rate this question:
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- 5.
The reaction graph below represents an ________ reaction.
- A.
Endothermic reaction
- B.
Exothermic reaction
Correct Answer
B. Exothermic reactionExplanation
The reaction graph shows a decrease in energy from the reactants to the products, indicating that energy is released during the reaction. This is characteristic of an exothermic reaction, where the products have lower energy than the reactants.Rate this question:
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- 6.
In the Potential Energy in a Chemical Reaction graph above, it can be observed that ________ have more potential energy.
- A.
The reactants
- B.
The products
- C.
Substance A
- D.
Substance AB
Correct Answer
A. The reactantsExplanation
The potential energy in a chemical reaction graph represents the energy stored in the system. In this case, the graph shows that the potential energy of the reactants is higher than that of the products. This indicates that the reactants have more potential energy.Rate this question:
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- 7.
When chemical bonds are broken and new substances are created a chemist states ______ has occurred.
- A.
A nuclear reaction
- B.
A chemical change
- C.
No change has occurred
- D.
Mass destruction
Correct Answer
B. A chemical changeExplanation
When chemical bonds are broken and new substances are created, a chemist states that a chemical change has occurred. This is because a chemical change refers to a process where the composition and properties of a substance are altered, resulting in the formation of new substances. In this case, the breaking of chemical bonds and the creation of new substances indicate a chemical reaction, which is a type of chemical change. Therefore, the correct answer is a chemical change.Rate this question:
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- 8.
Study the chemical equation below. Identify the chemical products and reactants. Mg + HCl à MgCl2 + H2 a. Reactants = Mg and Cl, Products = MgCl2 and H2 b. Reactants = Mg and HCl, Products = MgCl2 and H2 c. Reactants = MgCl2 and H2, Products = Mg and HCl d. Reactants = MgCl and H2, Products = MgCl2 and HCl
- A.
A
- B.
B
- C.
C
- D.
D
Correct Answer
B. BExplanation
The correct answer is b. In the given chemical equation, Mg and HCl are the reactants because they are the substances that undergo a chemical change. MgCl2 and H2 are the products because they are the substances that are formed as a result of the chemical reaction.Rate this question:
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- 9.
In this chemical formula for aluminum Sulfate, 3Al2(SO4)3, how many atoms of each element are indicated by the formula?
- A.
A.4 aluminum, 12 sulfur, and 12 oxygen atoms
- B.
6 aluminum, 9 sulfur, and 36 oxygen atoms
- C.
5 aluminum, 12 sulfur, and 48 oxygen atoms
- D.
6 aluminum, 9 sulfur, and 12 oxygen atoms
- 10.
In the formula for 6 molecules of sodium sulfate, 6Na2SO4, what is the subscript for the sulfur atom?
- A.
6
- B.
2
- C.
1
- D.
4
- 11.
Which of the following actions would probably speed up the chemical reaction between magnesium and hydrochloric acid?
- A.
Decrease the surface area of magnesium.
- B.
Raise the temperature of the hydrochloric acid.
- C.
Add an inhibitor
- D.
Decrease the mass of the magnesium
Correct Answer
B. Raise the temperature of the hydrochloric acid.Explanation
Raising the temperature of the hydrochloric acid would probably speed up the chemical reaction between magnesium and hydrochloric acid because increasing the temperature typically increases the rate of reaction. This is because higher temperatures provide more energy to the reactant particles, causing them to move faster and collide more frequently and with greater energy. As a result, more successful collisions occur, leading to a faster reaction rate.Rate this question:
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- 12.
Which of the following equation is a synthesis reaction?
- 2H2O à 2H2 + O2
- 2Ca + O2 à 2CaO
- Mg + 2HCl à MgCl2 + H2
- NaOH + HCl à NaCl + H2O
- A.
A
- B.
B
- C.
C
- D.
D
- 13.
Which of these equations is a double replacement reaction?
- 2H2O à 2H2 + O2
- 2Ca + O2 à 2CaO
- Mg + 2HCl à MgCl2 + H2
- 2NaOH + MgCl2 à 2NaCl + Mg(OH)2
- A.
A
- B.
B
- C.
C
- D.
D
- 14.
The chemical reaction that is the opposite of a synthesis reaction is the
- A.
Single Replacement
- B.
Decomposition
- C.
Double Replacement
- D.
Exothermic
Correct Answer
B. DecompositionExplanation
A synthesis reaction is a chemical reaction where two or more substances combine to form a more complex product. In contrast, a decomposition reaction is the opposite, where a complex substance breaks down into simpler substances. Therefore, the correct answer is "Decomposition" as it represents the opposite of a synthesis reaction.Rate this question:
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- 15.
A chemist adds more Sulfuric Acid solution to a beaker to speed up the double replacement reaction between Sodium Hydroxide and Sulfuric Acid. Which of the following factors did the chemist change to speed up the reaction?
- A.
Temperature
- B.
Concentration
- C.
Catalyst
- D.
Surface area
Correct Answer
B. ConcentrationExplanation
The chemist changed the concentration of the Sulfuric Acid solution to speed up the reaction. Increasing the concentration of a reactant increases the number of particles available for collision, which in turn increases the frequency of effective collisions. This leads to a higher reaction rate and faster reaction.Rate this question:
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- 16.
Chemical equation must be balanced to obey the
- A.
Octet rule.
- B.
Law of conservation of energy.
- C.
Law of conservation of mass.
- D.
Law of reactions
- 17.
Which of these equations is NOT balanced?
- SO3 à S + O2
- 2H2O à 2H2 + O2
- MnO4 à Mn + 2O2
- 2Cu + O2 à 2CuO
- A.
A
- B.
B
- C.
C
- D.
D
- 18.
Which of the following is a single replacement reaction?
- 2H2O à 2H2 + O2
- 2Ca + 02 à 2CaO
- Mg + 2HCl à MgCl2 + H2
- 2NaOH + MgCl2 à 2NaCl + Mg(OH)2
- A.
A
- B.
B
- C.
C
- D.
D
- 19.
In a chemical reaction it is noticed that a precipitate has formed in the test tube.The precipitate is a ____.
- A.
Liquid
- B.
Gas
- C.
Solid
- D.
Element
Correct Answer
C. SolidExplanation
In a chemical reaction, when a precipitate forms in a test tube, it indicates the formation of a solid. Precipitates are insoluble solids that are formed when two or more soluble substances react and produce an insoluble compound. This solid substance separates from the liquid solution and settles at the bottom of the test tube. Therefore, the correct answer is solid.Rate this question:
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- 20.
What coefficient is needed to replace the "?" that will then balance this chemical equation?2NaOH + MgCl2 à ? NaCl + Mg(OH)2
- A.
1
- B.
2
- C.
3
- D.
4
Correct Answer
B. 2Explanation
To balance the chemical equation, the coefficient of MgCl2 should be 2. This will ensure that there are equal numbers of atoms on both sides of the equation.Rate this question:
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- 21.
Which of the following is a decomposition reaction?
- 2H2O à 2H2 + O2
- 2Ca + 02 à 2CaO
- Mg + 2HCl à MgCl2 + H2
- 2NaOH + MgCl2 à 2NaCl + Mg(OH)2
- A.
A
- B.
B
- C.
C
- D.
D
- 22.
Which of the following is a double replacement reaction?
- 2H2O à 2H2 + O2
- 2Ca + 02 à 2CaO
- Mg + 2HCl à MgCl2 + H2
- 2NaOH + MgCl2 à 2NaCl + Mg(OH)2
- A.
A
- B.
B
- C.
C
- D.
D
- 23.
Which of the compounds in this reaction is a solid?
- 2NaOH (aq) + MgCl2 (aq) à 2NaCl (aq) + Mg(OH)2 (s)a) NaOHb) NaClc) Mg(OH)2d) MgCl2
- A.
A
- B.
B
- C.
C
- D.
D
- 24.
The reaction type notated as A + B --> ABrepresent a model for a ___________ reaction.
- A.
Synthesis
- B.
Decomposition
- C.
Single replacement
- D.
Double replacement
Correct Answer
A. SynthesisExplanation
The reaction type notated as A + B --> AB represents a synthesis reaction. In a synthesis reaction, two or more reactants combine to form a single product. In this case, reactant A and reactant B combine to form product AB.Rate this question:
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- 25.
Predict the products for this single replacement reaction: Mg + 2HCl à ________ + _______a) MgCl2 + Hb) MgCl + H2c) Cl2 + H2Mgd) MgH2 + Cl2e) MgCl2 + H2
- A.
A
- B.
B
- C.
C
- D.
D
- E.
E
Correct Answer
E. EExplanation
In a single replacement reaction, a more reactive element replaces a less reactive element in a compound. In this case, magnesium (Mg) is more reactive than hydrogen (H), so it will replace hydrogen in hydrochloric acid (HCl). The products of this reaction are magnesium chloride (MgCl2) and hydrogen gas (H2). Therefore, the correct answer is e) MgCl2 + H2.Rate this question:
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- 26.
Using this "Activity Series" of the elements to predict which reaction will NOT occur.Activity SeriesLithium (Most Active)PotassiumMagnesiumAluminumIronTinLead (Least Active)Reactions:a) Li + KCl à b) Mg + SnO àc) Fe + MgO àd) K + PbO à
- A.
A
- B.
B
- C.
C
- D.
D
Correct Answer
C. CExplanation
The reaction in option c (Fe + MgO) will not occur because iron (Fe) is less active than magnesium (Mg) in the activity series. According to the activity series, more active metals can displace less active metals from their compounds. Since magnesium is more active than iron, it can displace iron from its compound (FeO), but iron cannot displace magnesium from its compound (MgO). Therefore, the reaction between iron and magnesium oxide will not occur.Rate this question:
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Correct Answer
B. 6 aluminum, 9 sulfur, and 36 oxygen atoms
B. 6 aluminum, 9 sulfur, and 36 oxygen atoms
Explanation
The chemical formula for aluminum sulfate, 3Al2(SO4)3, indicates that there are 6 atoms of aluminum, 9 atoms of sulfur, and 36 atoms of oxygen in the compound.
The chemical formula for aluminum sulfate, 3Al2(SO4)3, indicates that there are 6 atoms of aluminum, 9 atoms of sulfur, and 36 atoms of oxygen in the compound.
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Correct Answer
C. 1
C. 1
Explanation
In the formula for 6 molecules of sodium sulfate, 6Na2SO4, the subscript for the sulfur atom is 1. This means that there is only one sulfur atom present in each molecule of sodium sulfate.
In the formula for 6 molecules of sodium sulfate, 6Na2SO4, the subscript for the sulfur atom is 1. This means that there is only one sulfur atom present in each molecule of sodium sulfate.
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Correct Answer
B. B
B. B
Explanation
The equation 2Ca + O2 à 2CaO is a synthesis reaction because it involves the combination of two or more substances to form a single compound. In this case, calcium (Ca) combines with oxygen (O2) to form calcium oxide (CaO).
The equation 2Ca + O2 à 2CaO is a synthesis reaction because it involves the combination of two or more substances to form a single compound. In this case, calcium (Ca) combines with oxygen (O2) to form calcium oxide (CaO).
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Correct Answer
D. D
D. D
Explanation
The equation 2NaOH + MgCl2 à 2NaCl + Mg(OH)2 is a double replacement reaction because two compounds (NaOH and MgCl2) exchange their positive and negative ions to form two new compounds (NaCl and Mg(OH)2). This type of reaction is characterized by the swapping of ions between two compounds.
The equation 2NaOH + MgCl2 à 2NaCl + Mg(OH)2 is a double replacement reaction because two compounds (NaOH and MgCl2) exchange their positive and negative ions to form two new compounds (NaCl and Mg(OH)2). This type of reaction is characterized by the swapping of ions between two compounds.
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Correct Answer
C. Law of conservation of mass.
C. Law of conservation of mass.
Explanation
The correct answer is the law of conservation of mass. This law states that matter cannot be created or destroyed in a chemical reaction, only rearranged. Therefore, in a balanced chemical equation, the number of atoms of each element on both sides of the equation must be the same, ensuring that mass is conserved. The octet rule refers to the arrangement of electrons in atoms, the law of conservation of energy relates to the conservation of energy in a system, and the law of reactions is not a recognized scientific principle.
The correct answer is the law of conservation of mass. This law states that matter cannot be created or destroyed in a chemical reaction, only rearranged. Therefore, in a balanced chemical equation, the number of atoms of each element on both sides of the equation must be the same, ensuring that mass is conserved. The octet rule refers to the arrangement of electrons in atoms, the law of conservation of energy relates to the conservation of energy in a system, and the law of reactions is not a recognized scientific principle.
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Correct Answer
A. A
A. A
Explanation
Option a is not a balanced equation because the number of atoms on both sides of the equation is not equal. On the left side, there is one sulfur atom and three oxygen atoms, while on the right side, there is only one sulfur atom and two oxygen atoms. Therefore, option a is the correct answer as it is the only equation that is not balanced.
Option a is not a balanced equation because the number of atoms on both sides of the equation is not equal. On the left side, there is one sulfur atom and three oxygen atoms, while on the right side, there is only one sulfur atom and two oxygen atoms. Therefore, option a is the correct answer as it is the only equation that is not balanced.
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Correct Answer
C. C
C. C
Explanation
A single replacement reaction is a type of chemical reaction where an element replaces another element in a compound. In the given options, the reaction "Mg + 2HCl à MgCl2 + H2" is a single replacement reaction because magnesium (Mg) replaces hydrogen (H) in hydrochloric acid (HCl) to form magnesium chloride (MgCl2) and hydrogen gas (H2).
A single replacement reaction is a type of chemical reaction where an element replaces another element in a compound. In the given options, the reaction "Mg + 2HCl à MgCl2 + H2" is a single replacement reaction because magnesium (Mg) replaces hydrogen (H) in hydrochloric acid (HCl) to form magnesium chloride (MgCl2) and hydrogen gas (H2).
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Correct Answer
A. A
A. A
Explanation
The given correct answer is "a" because the reaction 2H2O à 2H2 + O2 represents a decomposition reaction. In this reaction, water (H2O) is broken down into its constituent elements, hydrogen gas (H2) and oxygen gas (O2), through the application of heat or electricity. Therefore, it is a decomposition reaction.
The given correct answer is "a" because the reaction 2H2O à 2H2 + O2 represents a decomposition reaction. In this reaction, water (H2O) is broken down into its constituent elements, hydrogen gas (H2) and oxygen gas (O2), through the application of heat or electricity. Therefore, it is a decomposition reaction.
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Correct Answer
D. D
D. D
Explanation
The reaction 2NaOH + MgCl2 → 2NaCl + Mg(OH)2 is a double replacement reaction because the two compounds (NaOH and MgCl2) exchange their ions to form two new compounds (NaCl and Mg(OH)2). In this reaction, the sodium ions from NaOH combine with the chloride ions from MgCl2 to form NaCl, while the hydroxide ions from NaOH combine with the magnesium ions from MgCl2 to form Mg(OH)2.
The reaction 2NaOH + MgCl2 → 2NaCl + Mg(OH)2 is a double replacement reaction because the two compounds (NaOH and MgCl2) exchange their ions to form two new compounds (NaCl and Mg(OH)2). In this reaction, the sodium ions from NaOH combine with the chloride ions from MgCl2 to form NaCl, while the hydroxide ions from NaOH combine with the magnesium ions from MgCl2 to form Mg(OH)2.
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Correct Answer
C. C
C. C
Explanation
In this reaction, the compound Mg(OH)2 is a solid. This is indicated by the "(s)" after its formula, which stands for solid. The other compounds, NaOH, NaCl, and MgCl2, are all in the aqueous state, indicated by "(aq)", which means they are dissolved in water.
In this reaction, the compound Mg(OH)2 is a solid. This is indicated by the "(s)" after its formula, which stands for solid. The other compounds, NaOH, NaCl, and MgCl2, are all in the aqueous state, indicated by "(aq)", which means they are dissolved in water.
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