73. a + bc → ac + b is what type?
a. synthesis
b. decomposition
c. single replacement
d. double replacement

74. ab + cd → ad + cb is what type?
a. synthesis
b. decomposition
c. single replacement
d. double replacement

75. which bonds break during chemical reactions?
a. nuclear
b. chemical
c. magnetic
d. electrical

76. what is the minimum energy needed to start a reaction?
a. output energy
b. heat
c. activation energy
d. nuclear energy

77. which is an example of energy being absorbed?
a. fire burning
b. ice melting
c. wood rotting
d. metal rusting

78. which is not evidence of a chemical reaction?
a. gas produced
b. heat released
c. new substance formed
d. change in shape

79. which reaction releases energy to the surroundings?
a. endothermic
b. exothermic
c. neutral
d. decomposition

80. when hydrogen reacts with oxygen, what is formed?
a. carbon dioxide
b. nitrogen
c. water
d. oxygen

balancing & counting atoms (81-100)

81. how many hydrogen atoms are in 2h₂o?
a. 2
b. 4
c. 6
d. 8

82. how many oxygen atoms are in ca₃(po₄)₂?
a. 2
b. 4
c. 6
d. 8

83. what tells the number of atoms in a formula?
a. coefficient
b. subscript
c. symbol
d. arrow

84. how many aluminum atoms are in al₂o₃?
a. 1
b. 2
c. 3
d. 5

85. what do coefficients change when balancing?
a. type of atom
b. number of molecules
c. bond type
d. charge

86. which equation is balanced?
a. h₂ + o₂ → h₂o
b. 2h₂ + o₂ → 2h₂o
c. h₂ + 2o₂ → 2h₂o
d. 4h + o → h₂o

Question

73. a + bc → ac + b is what type?
a. synthesis
b. decomposition
c. single replacement
d. double replacement

74. ab + cd → ad + cb is what type?
a. synthesis
b. decomposition
c. single replacement
d. double replacement

75. which bonds break during chemical reactions?
a. nuclear
b. chemical
c. magnetic
d. electrical

76. what is the minimum energy needed to start a reaction?
a. output energy
b. heat
c. activation energy
d. nuclear energy

77. which is an example of energy being absorbed?
a. fire burning
b. ice melting
c. wood rotting
d. metal rusting

78. which is not evidence of a chemical reaction?
a. gas produced
b. heat released
c. new substance formed
d. change in shape

79. which reaction releases energy to the surroundings?
a. endothermic
b. exothermic
c. neutral
d. decomposition

80. when hydrogen reacts with oxygen, what is formed?
a. carbon dioxide
b. nitrogen
c. water
d. oxygen

balancing & counting atoms (81-100)

81. how many hydrogen atoms are in 2h₂o?
a. 2
b. 4
c. 6
d. 8

82. how many oxygen atoms are in ca₃(po₄)₂?
a. 2
b. 4
c. 6
d. 8

83. what tells the number of atoms in a formula?
a. coefficient
b. subscript
c. symbol
d. arrow

84. how many aluminum atoms are in al₂o₃?
a. 1
b. 2
c. 3
d. 5

85. what do coefficients change when balancing?
a. type of atom
b. number of molecules
c. bond type
d. charge

86. which equation is balanced?
a. h₂ + o₂ → h₂o
b. 2h₂ + o₂ → 2h₂o
c. h₂ + 2o₂ → 2h₂o
d. 4h + o → h₂o

Accepted Answer

Let's solve these chemistry (Natural Science - Chemistry) questions one by one:

### Question 73: $ A + BC
ightarrow AC + B $ is what type?
#### Explanation:
## Step1: Recall reaction types
Synthesis: $ A + B
ightarrow AB $; Decomposition: $ AB
ightarrow A + B $; Single replacement: $ A + BC
ightarrow AC + B $ (one element replaces another in a compound); Double replacement: $ AB + CD
ightarrow AD + CB $ (ions swap).
## Step2: Match the given reaction
The reaction $ A + BC
ightarrow AC + B $ fits single replacement (one element replaces another in the compound $ BC $).
# Answer: C. Single replacement

### Question 74: $ AB + CD
ightarrow AD + CB $ is what type?
#### Explanation:
## Step1: Recall reaction types
Double replacement reactions involve swapping ions between two compounds (formula: $ AB + CD
ightarrow AD + CB $).
## Step2: Match the given reaction
The reaction $ AB + CD
ightarrow AD + CB $ matches the double replacement pattern.
# Answer: D. Double replacement

### Question 75: Which bonds break during chemical reactions?
#### Explanation:
## Step1: Analyze bond types
Nuclear bonds: involve atomic nuclei (not broken in chemical reactions); Chemical bonds: hold atoms in molecules/compounds, broken during chemical reactions; Magnetic/electrical bonds: not relevant to chemical reaction bond breaking.
## Step2: Conclude
Chemical bonds break during chemical reactions.
# Answer: B. Chemical

### Question 76: What is the minimum energy needed to start a reaction?
#### Explanation:
## Step1: Recall energy terms
Output energy: energy released; Heat: energy transfer; Activation energy: minimum energy to start a reaction; Nuclear energy: energy from atomic nuclei.
## Step2: Identify the term
Activation energy is the minimum energy required to initiate a reaction.
# Answer: C. Activation energy

### Question 77: Which is an example of energy being absorbed?
#### Explanation:
## Step1: Analyze processes
Fire burning: releases energy (exothermic); Ice melting: absorbs heat (endothermic, energy absorbed to melt ice); Wood rotting: releases energy (exothermic decay); Metal rusting: releases energy (exothermic oxidation).
## Step2: Identify endothermic process
Ice melting absorbs energy (heat) to change from solid to liquid.
# Answer: B. Ice melting

### Question 78: Which is NOT evidence of a chemical reaction?
#### Explanation:
## Step1: Recall chemical reaction evidence
Gas produced, heat released, new substance formed are all chemical reaction evidence. Change in shape (e.g., bending a metal) is a physical change (no new substance), not chemical reaction evidence.
## Step2: Conclude
Change in shape is not evidence of a chemical reaction.
# Answer: D. Change in shape

### Question 79: Which reaction releases energy to the surroundings?
#### Explanation:
## Step1: Recall energy terms
Endothermic: absorbs energy from surroundings; Exothermic: releases energy to surroundings; Neutral: no net energy change (not a reaction type); Decomposition: a reaction type (can be exo/endo, but the term for releasing energy is exothermic).
## Step2: Identify the term
Exothermic reactions release energy to the surroundings.
# Answer: B. Exothermic

### Question 80: When hydrogen reacts with oxygen, what is formed?
#### Explanation:
## Step1: Recall the reaction
Hydrogen ($ H_2 $) + Oxygen ($ O_2 $) → Water ($ H_2O $) (reaction: $ 2H_2 + O_2
ightarrow 2H_2O $). Carbon dioxide forms from carbon + oxygen; Nitrogen is not a product here; Oxygen is a reactant, not product.
## Step2: Identify the product
Water is formed when $ H_2 $ reacts with $ O_2 $.
# Answer: C. Water

### Question 81: How many hydrogen atoms are in $ 2H_2O $?
#### Explanation:
## Step1: Analyze the formula
In $ H_2O $, each molecule has 2 H atoms. The coefficient 2 means 2 molecules of $ H_2O $.
## Step2: Calculate total H atoms
Total H atoms = $ 2 $ (molecules) $ \times 2 $ (H per $ H_2O $) = $ 4 $.
# Answer: B. 4

### Question 82: How many oxygen atoms are in $ Ca_3(PO_4)_2 $?
#### Explanation:
## Step1: Analyze the formula
In $ (PO_4)_2 $, the subscript 2 applies to $ PO_4 $. Each $ PO_4 $ has 4 O atoms, so $ 2 \times 4 = 8 $? Wait, no: $ (PO_4)_2 $ means 2 phosphate groups. Wait, no: $ Ca_3(PO_4)_2 $: inside the parentheses, $ PO_4 $ has 4 O, and the subscript 2 outside multiplies the entire $ PO_4 $. So O atoms: $ 4 \times 2 = 8 $? Wait, no, wait: $ Ca_3(PO_4)_2 $: $ PO_4 $ is a group, subscript 2 means 2 of those groups. Each $ PO_4 $ has 4 O, so $ 2 \times 4 = 8 $? Wait, no, the options are 2,4,6,8. Wait, maybe I miscalculated. Wait, $ (PO_4)_2 $: P: 2, O: 4×2=8? Wait, no, the formula is $ Ca_3(PO_4)_2 $. Let's count: Ca: 3, P: 2, O: 4×2=8. So O atoms: 8? Wait, but the options have D. 8. Wait, maybe the question is $ Ca_3(PO_4)_2 $, so O: 4×2=8.
## Step2: Calculate O atoms
Each $ PO_4 $ has 4 O, and there are 2 $ PO_4 $ groups (due to the subscript 2 outside the parentheses). So total O atoms: $ 4 \times 2 = 8 $.
# Answer: D. 8

### Question 83: What tells the number of atoms in a formula?
#### Explanation:
## Step1: Recall formula notation
Coefficient: number of molecules (e.g., 2 in $ 2H_2O $); Subscript: number of atoms of an element in a molecule (e.g., 2 in $ H_2O $ for H); Symbol: element identity; Arrow: reaction direction.
## Step2: Identify the term
Subscript tells the number of atoms of an element in a formula (e.g., $ H_2O $: subscript 2 means 2 H atoms).
# Answer: B. Subscript

### Question 84: How many aluminum atoms are in $ Al_2O_3 $?
#### Explanation:
## Step1: Analyze the formula
In $ Al_2O_3 $, the subscript 2 follows Al, so there are 2 Al atoms.
## Step2: Count Al atoms
Subscript 2 after Al means 2 aluminum atoms.
# Answer: B. 2

### Question 85: What do coefficients change when balancing?
#### Explanation:
## Step1: Recall balancing equations
Coefficients are placed in front of molecules (e.g., 2 in $ 2H_2O $). They change the number of molecules (e.g., 2 $ H_2O $ means 2 molecules). They do not change the type of atom (atoms are conserved), bond type, or "change" (vague).
## Step2: Identify the effect
Coefficients change the number of molecules (e.g., 2 $ H_2O $ is 2 molecules of water).
# Answer: B. Number of molecules

### Question 86: Which equation is balanced?
#### Explanation:
## Step1: Balance each equation
- Option A: $ H_2 + O_2
ightarrow H_2O $. Left: H=2, O=2; Right: H=2, O=1. Not balanced.
- Option B: $ 2H_2 + O_2
ightarrow 2H_2O $. Left: H=4, O=2; Right: H=4, O=2. Balanced.
- Option C: $ H_2 + 2O_2
ightarrow 2H_2O $. Left: H=2, O=4; Right: H=4, O=2. Not balanced.
- Option D: $ 4H + O
ightarrow H_2O $. Atoms are not in molecule form (incorrect notation, and H:4 vs 2, O:1 vs 1). Not balanced.
## Step2: Identify balanced equation
Option B has equal numbers of H and O on both sides.
# Answer: B. $ 2H_2 + O_2
ightarrow 2H_2O $

### Final Answers (in order of questions 73–86):
73. C. Single replacement
74. D. Double replacement
75. B. Chemical
76. C. Activation energy
77. B. Ice melting
78. D. Change in shape
79. B. Exothermic
80. C. Water
81. B. 4
82. D. 8
83. B. Subscript
84. B. 2
85. B. Number of molecules
86. B. $ 2H_2 + O_2
ightarrow 2H_2O $

Sovi.AI - AI Math Tutor

QUESTION IMAGE

Question

Explanation:

Question 73: \( A + BC

Step1: Recall reaction types

Step2: Match the given reaction

Step1: Recall reaction types

Step2: Match the given reaction

Step1: Analyze bond types

Step2: Conclude

Answer:

Question 74: \( AB + CD