9. a molecule consisting of a central atom surrounded by two bonding pairs and two non-bonding (lone) pairs of electrons will be
a. linear
b. tetrahedral
c. bent
d. trigonal pyramidal
e. trigonal planar

10. which of the molecules, $\text{co}_2$, $\text{h}_2\text{o}$, $\text{nh}_3$, and $\text{bf}_3$, will be polar?
a. $\text{co}_2$, $\text{nh}_3$, and $\text{bf}_3$
b. $\text{h}_2\text{o}$ and $\text{nh}_3$
c. $\text{co}_2$, $\text{h}_2\text{o}$ and $\text{nh}_3$
d. $\text{h}_2\text{o}$ and $\text{bf}_3$
e. $\text{co}_2$ and $\text{bf}_3$

11. an endothermic reaction is one where
a. heat is transferred from the surroundings into a system
b. heat is transferred from a system into the surroundings
c. kinetic energy is transformed into potential energy
d. there is no transfer of heat
e. none of the above

12. we can communicate the energy changes obtained from empirical studies by
a. including an energy value as a term in the thermochemical equation
b. writing a chemical equation and stating its enthalpy change
c. stating the molar enthalpy of a specific reaction
d. drawing a chemical potential energy diagram
e. any of the above

13. the heat released during the combustion of $\text{c}_3\text{h}_8(\text{g})$ (propane) to produce $\text{co}_2$ (carbon dioxide) gas and water vapour is $2222\text{ kj/mol}$ of $\text{c}_3\text{h}_8(\text{g})$. which of the following is the correct chemical equation for the reaction?
a. $\text{c}_3\text{h}_8(\text{g}) + 5\text{o}_2(\text{g}) \
ightarrow 3\text{co}_2(\text{g}) + 4\text{h}_2\text{o}(\text{g}) \quad \delta h = +2222\text{ kj}$
b. $\text{c}_3\text{h}_8(\text{g}) + 5\text{o}_2(\text{g}) + 2222\text{ kj} \
ightarrow 4\text{h}_2\text{o}(\text{g}) + 3\text{co}_2(\text{g})$
c. $\text{c}_3\text{h}_8(\text{g}) + 5\text{o}_2(\text{g}) \
ightarrow 3\text{co}_2(\text{g}) + 4\text{h}_2\text{o}(\text{g}) + 2222\text{ kj}$
d. $3\text{co}_2(\text{g}) + 4\text{h}_2\text{o}(\text{g}) \
ightarrow 5\text{o}_2(\text{g}) + \text{c}_3\text{h}_8(\text{g}) \quad \delta h = -2222\text{ kj}$
e. none of the above

14. an effective collision is
a. a collision where the particles have sufficient energy to react
b. a collision where the particles collide with beneficial collision geometry
c. a collision where old bonds are broken and new bonds are formed
d. both a and b are correct
e. all of a, b, and c are correct

15. the amount of energy required for a reaction to begin is known as
a. enthalpy change
b. kinetic energy
c. reaction energy
d. activation energy
e. potential energy

16. when a reaction is broken down into a number of elementary steps, this is known as a
a. reaction progression
b. reaction step
c. reaction mechanism
d. none of the above
e. reaction pattern

Question

9. a molecule consisting of a central atom surrounded by two bonding pairs and two non-bonding (lone) pairs of electrons will be
a. linear
b. tetrahedral
c. bent
d. trigonal pyramidal
e. trigonal planar

10. which of the molecules, $\text{co}_2$, $\text{h}_2\text{o}$, $\text{nh}_3$, and $\text{bf}_3$, will be polar?
a. $\text{co}_2$, $\text{nh}_3$, and $\text{bf}_3$
b. $\text{h}_2\text{o}$ and $\text{nh}_3$
c. $\text{co}_2$, $\text{h}_2\text{o}$ and $\text{nh}_3$
d. $\text{h}_2\text{o}$ and $\text{bf}_3$
e. $\text{co}_2$ and $\text{bf}_3$

11. an endothermic reaction is one where
a. heat is transferred from the surroundings into a system
b. heat is transferred from a system into the surroundings
c. kinetic energy is transformed into potential energy
d. there is no transfer of heat
e. none of the above

12. we can communicate the energy changes obtained from empirical studies by
a. including an energy value as a term in the thermochemical equation
b. writing a chemical equation and stating its enthalpy change
c. stating the molar enthalpy of a specific reaction
d. drawing a chemical potential energy diagram
e. any of the above

13. the heat released during the combustion of $\text{c}_3\text{h}_8(\text{g})$ (propane) to produce $\text{co}_2$ (carbon dioxide) gas and water vapour is $2222\text{ kj/mol}$ of $\text{c}_3\text{h}_8(\text{g})$. which of the following is the correct chemical equation for the reaction?
a. $\text{c}_3\text{h}_8(\text{g}) + 5\text{o}_2(\text{g}) \
ightarrow 3\text{co}_2(\text{g}) + 4\text{h}_2\text{o}(\text{g}) \quad \delta h = +2222\text{ kj}$
b. $\text{c}_3\text{h}_8(\text{g}) + 5\text{o}_2(\text{g}) + 2222\text{ kj} \
ightarrow 4\text{h}_2\text{o}(\text{g}) + 3\text{co}_2(\text{g})$
c. $\text{c}_3\text{h}_8(\text{g}) + 5\text{o}_2(\text{g}) \
ightarrow 3\text{co}_2(\text{g}) + 4\text{h}_2\text{o}(\text{g}) + 2222\text{ kj}$
d. $3\text{co}_2(\text{g}) + 4\text{h}_2\text{o}(\text{g}) \
ightarrow 5\text{o}_2(\text{g}) + \text{c}_3\text{h}_8(\text{g}) \quad \delta h = -2222\text{ kj}$
e. none of the above

14. an effective collision is
a. a collision where the particles have sufficient energy to react
b. a collision where the particles collide with beneficial collision geometry
c. a collision where old bonds are broken and new bonds are formed
d. both a and b are correct
e. all of a, b, and c are correct

15. the amount of energy required for a reaction to begin is known as
a. enthalpy change
b. kinetic energy
c. reaction energy
d. activation energy
e. potential energy

16. when a reaction is broken down into a number of elementary steps, this is known as a
a. reaction progression
b. reaction step
c. reaction mechanism
d. none of the above
e. reaction pattern

Accepted Answer

{ "quality": "clear", "question_count": 8, "skills_matched": [ "direct_cot", "multiple_choice_formatter", "explain_then_answer", "tutor", "mastery_adaptive_brevity" ], "needs_drawing": false, "concepts_used": [ "Combustion Reactions" ], "new_concepts": [ "VSEPR Theory", "Molecular Polarity", "Reaction Mechanisms" ], "current_concepts": [ "VSEPR Theory", "Molecular Polarity", "Endothermic Reactions", "Thermochemical Equations", "Combustion Reactions", "Collision Theory", "Activation Energy", "Reaction Mechanisms" ] } ## Question 9: Molecular Geometry A central atom with two bonding pairs and two non-bonding (lone) pairs has a steric number of 4. According to VSEPR theory, the electron-pair geometry is tetrahedral, but the molecular shape formed by the atoms is bent (like water, $\text{H}_2\text{O}$). ## Question 10: Molecular Polarity Let's analyze the polarity of each molecule: - $\text{CO}_2$: Linear and symmetrical, so dipoles cancel (non-polar). - $\text{H}_2\text{O}$: Bent and asymmetrical, dipoles do not cancel (polar). - $\text{NH}_3$: Trigonal pyramidal and asymmetrical, dipoles do not cancel (polar). - $\text{BF}_3$: Trigonal planar and symmetrical, dipoles cancel (non-polar). Thus, $\text{H}_2\text{O}$ and $\text{NH}_3$ are polar. ## Question 11: Endothermic Reactions An endothermic reaction is defined as a chemical process where thermal energy (heat) is absorbed by the system from its surroundings. ## Question 12: Communicating Energy Changes Energy changes in chemical reactions can be communicated in several standard ways: - Including energy as a reactant or product term in a thermochemical equation. - Writing a balanced equation and stating its enthalpy change ($\Delta H$) next to it. - Stating the molar enthalpy of a specific substance. - Drawing a potential energy diagram. Since all options (a, b, c, and d) are valid scientific methods, the correct choice is "any of the above". ## Question 13: Combustion of Propane Using the **Combustion Reactions** knowledge point: The combustion of propane ($\text{C}_3\text{H}_8$) releases $2222\text{ kJ/mol}$ of heat. Since heat is released, the reaction is exothermic, meaning: - The enthalpy change must be negative: $\Delta H = -2222\text{ kJ}$. - Alternatively, heat can be written as a product: $\text{C}_3\text{H}_8(g) + 5\text{O}_2(g) ightarrow 3\text{CO}_2(g) + 4\text{H}_2\text{O}(g) + 2222\text{ kJ}$. Looking at the options, option (c) correctly represents this by placing $2222\text{ kJ}$ on the product side of the equation. ## Question 14: Collision Theory According to collision theory, for a collision between reactant particles to be effective (resulting in a reaction), two conditions must be met: - The particles must collide with sufficient kinetic energy to overcome the activation energy barrier (statement a). - The particles must collide with the correct spatial orientation or geometry (statement b). Therefore, both a and b are correct. ## Question 15: Activation Energy The minimum amount of energy required to initiate a chemical reaction by overcoming the potential energy barrier is defined as the activation energy ($E_a$). ## Question 16: Reaction Mechanisms When a complex chemical reaction is broken down into a sequence of simpler, individual elementary steps, this sequence is known as a reaction mechanism. ## Question 9 a. Linear

b. Tetrahedral

c. Bent

d. Trigonal pyramidal

e. Trigonal planar ## Question 10 a. $\text{CO}_2$, $\text{NH}_3$, and $\text{BF}_3$

b. $\text{H}_2\text{O}$ and $\text{NH}_3$

c. $\text{CO}_2$, $\text{H}_2\text{O}$ and $\text{NH}_3$

d. $\text{H}_2\text{O}$ and $\text{BF}_3$

e. $\text{CO}_2$ and $\text{BF}_3$ ## Question 11 a. heat is transferred from the surroundings into a system

b. heat is transferred from a system into the surroundings

c. kinetic energy is transformed into potential energy

d. there is no transfer of heat

e. none of the above ## Question 12 a. including an energy value as a term in the thermochemical equation

b. writing a chemical equation and stating its enthalpy change

c. stating the molar enthalpy of a specific reaction

d. drawing a chemical potential energy diagram

e. any of the above ## Question 13 a. $\text{C}_3\text{H}_8(g) + 5\text{O}_2(g) ightarrow 3\text{CO}_2(g) + 4\text{H}_2\text{O}(g) \quad \Delta H = +2222\text{ kJ}$

b. $\text{C}_3\text{H}_8(g) + 5\text{O}_2(g) + 2222\text{ kJ} ightarrow 4\text{H}_2\text{O}(g) + 3\text{CO}_2(g)$

c. $\text{C}_3\text{H}_8(g) + 5\text{O}_2(g) ightarrow 3\text{CO}_2(g) + 4\text{H}_2\text{O}(g) + 2222\text{ kJ}$

d. $\text{3CO}_2(g) + 4\text{H}_2\text{O}(g) ightarrow 5\text{O}_2(g) + \text{C}_3\text{H}_8(g) \quad \Delta H = -2222\text{ kJ}$

e. none of the above ## Question 14 a. a collision where the particles have sufficient energy to react

b. a collision where the particles collide with beneficial collision geometry

c. a collision where old bonds are broken and new bonds are formed

d. Both a and b are correct

e. All of a, b, and c are correct ## Question 15 a. enthalpy change

b. kinetic energy

c. reaction energy

d. activation energy

e. potential energy ## Question 16 a. reaction progression

b. reaction step

c. reaction mechanism

d. none of the above

e. reaction pattern

{ "subject": "Natural Science", "question_type": "Multiple Choice", "knowledge_point": [ "Natural Science", "Chemistry", "Chemical Kinetics and Thermochemistry" ] }

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QUESTION IMAGE

Question

Explanation:

Question 9: Molecular Geometry

Question 10: Molecular Polarity

Question 11: Endothermic Reactions

Question 12: Communicating Energy Changes

Question 13: Combustion of Propane

Question 14: Collision Theory

Question 15: Activation Energy

Question 16: Reaction Mechanisms

Answer:

Question 9

Question 10

Question 11

Question 12

Question 13

Question 14

Question 15

Question 16