Podcast
Questions and Answers
What is a characteristic of physical changes?
What is a characteristic of physical changes?
- They do not produce new chemical substances. (correct)
- They always involve thermal energy transfer.
- They are often difficult to reverse.
- They form new substances with different properties.
Which of the following is an example of an endothermic reaction?
Which of the following is an example of an endothermic reaction?
- Thermal decomposition (correct)
- Neutralisation
- Combustion
- Oxidation
What happens to the energy of the system during an exothermic reaction?
What happens to the energy of the system during an exothermic reaction?
- The energy of the system increases.
- The energy of the system decreases. (correct)
- The energy of the system remains constant.
- The energy of the system fluctuates unpredictably.
What type of energy change occurs in most chemical reactions?
What type of energy change occurs in most chemical reactions?
What does a reaction pathway diagram illustrate?
What does a reaction pathway diagram illustrate?
Which of the following is NOT a sign that a chemical change has occurred?
Which of the following is NOT a sign that a chemical change has occurred?
What is the energy change during an endothermic reaction?
What is the energy change during an endothermic reaction?
Which of the following best describes the nature of energy transfer in exothermic reactions?
Which of the following best describes the nature of energy transfer in exothermic reactions?
What is the term used to describe the minimum amount of energy required for a successful collision in a chemical reaction?
What is the term used to describe the minimum amount of energy required for a successful collision in a chemical reaction?
In terms of enthalpy change, what sign value is typically associated with exothermic reactions?
In terms of enthalpy change, what sign value is typically associated with exothermic reactions?
Which process is always endothermic, requiring energy input from the surroundings?
Which process is always endothermic, requiring energy input from the surroundings?
What happens to the enthalpy change (ΔH) value in a reaction when more energy is released through bond formation than is absorbed during bond breaking?
What happens to the enthalpy change (ΔH) value in a reaction when more energy is released through bond formation than is absorbed during bond breaking?
If a reaction has a high activation energy, how does this affect the rate of the reaction?
If a reaction has a high activation energy, how does this affect the rate of the reaction?
Which statement correctly describes the relationship between bond breaking and the enthalpy change?
Which statement correctly describes the relationship between bond breaking and the enthalpy change?
In a chemical equation, if the formation of products results in a large amount of energy being released, what classification is given to the reaction?
In a chemical equation, if the formation of products results in a large amount of energy being released, what classification is given to the reaction?
What is the expected enthalpy change (ΔH) for an endothermic reaction?
What is the expected enthalpy change (ΔH) for an endothermic reaction?
Flashcards
Physical Change
Physical Change
A change that does not create new substances; often easily reversible.
Chemical Change
Chemical Change
A change that creates new substances with different properties; usually hard to reverse.
Exothermic Reaction
Exothermic Reaction
A reaction that releases heat to the surroundings.
Endothermic Reaction
Endothermic Reaction
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Reaction Pathway Diagram
Reaction Pathway Diagram
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Reactants
Reactants
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Products
Products
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Energy Change
Energy Change
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Activation Energy (Ea)
Activation Energy (Ea)
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What is the relationship between activation energy and reaction rate?
What is the relationship between activation energy and reaction rate?
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Enthalpy Change (ΔH)
Enthalpy Change (ΔH)
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Bond Breaking
Bond Breaking
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Bond Forming
Bond Forming
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How to calculate ΔH
How to calculate ΔH
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Study Notes
Photosynthesis
- Photosynthesis is the process by which plants use sunlight to synthesize foods from carbon dioxide and water.
- Sunlight is the energy source for this process.
- The process of photosynthesis is vital for life on Earth as it produces oxygen.
Physical Changes
- Physical changes do not create new substances.
- Examples include melting, evaporating, dissolving, mixing, crushing, and shredding.
- These changes are often easily reversed.
Chemical Changes
- Chemical changes result in the formation of new substances with different properties than the original substances.
- Examples include burning, rotting, baking, rusting, using a battery, digestion, souring, exploding fireworks, cooking an egg, and photosynthesis.
- Chemical changes are usually difficult to reverse.
- Signs of chemical changes include color changes, precipitate formation, gas bubbles, and energy changes.
Exothermic Reactions
- Exothermic reactions release energy to the surroundings.
- The energy change for an exothermic reaction is negative.
- Examples are burning wood, water and acid reaction, campfire, rusting iron, and Nuclear fission.
Endothermic Reactions
- Endothermic reactions absorb energy from the surroundings.
- The energy change for an endothermic reaction is positive.
- Examples include instant cold packs, cooking an egg, and photosynthesis.
Reaction Pathway Diagrams
- Reaction pathway diagrams show the energy changes during a chemical reaction.
- The y-axis displays the energy, and the x-axis represents the progress of the reaction.
- The difference between the energy of reactants and products indicates the overall energy change.
Enthalpy Change & Activation Energy
- Enthalpy change (ΔH) is the transfer of thermal energy during a reaction.
- Activation energy (Ea) is the minimum energy needed for a reaction to occur.
- Different reactions have different activation energies.
Bond Breaking & Bond Forming
- Bond breaking is an endothermic process.
- Bond forming is an exothermic process.
- Enthalpy change (ΔH) is calculated by subtracting the energy given out from the energy taken in.
Examples of Chemical Reactions (with data)
- H₂ + Cl₂ → 2HCl (Bond Energies: H-H = 436 kJ/mol, Cl-Cl = 243 kJ/mol, H-Cl = 432 kJ/mol)
- 2HBr → H₂ + Br₂ (Bond Energies: H-Br = 366 kJ/mol, H-H = 436 kJ/mol, Br-Br = 193 kJ/mol)
Types of Reaction & Bond Energies
- Examples will vary according to the specific questions/data provided.
- The overall process involves calculating the sum of the energy required to break original bonds and the energy released in forming new bonds, to determine if the reaction is exothermic or endothermic.
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