Photosynthesis and Chemical Changes Quiz

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Questions and Answers

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?

Thermal decomposition (correct)

Neutralisation

Combustion

Oxidation

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?

Most chemical reactions are exothermic. Signup and view all the answers

What does a reaction pathway diagram illustrate?

The energy changes of reactants and products. Signup and view all the answers

Which of the following is NOT a sign that a chemical change has occurred?

Evaporation of a liquid. Signup and view all the answers

What is the energy change during an endothermic reaction?

The energy change is positive. Signup and view all the answers

Which of the following best describes the nature of energy transfer in exothermic reactions?

Energy is transferred to the surroundings. Signup and view all the answers

What is the term used to describe the minimum amount of energy required for a successful collision in a chemical reaction?

Activation energy Signup and view all the answers

In terms of enthalpy change, what sign value is typically associated with exothermic reactions?

Negative Signup and view all the answers

Which process is always endothermic, requiring energy input from the surroundings?

Bond breaking Signup and view all the answers

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?

ΔH becomes negative Signup and view all the answers

If a reaction has a high activation energy, how does this affect the rate of the reaction?

It lowers the rate Signup and view all the answers

Which statement correctly describes the relationship between bond breaking and the enthalpy change?

Bond breaking requires energy, thus it contributes positively to the enthalpy change. Signup and view all the answers

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?

Exothermic Signup and view all the answers

What is the expected enthalpy change (ΔH) for an endothermic reaction?

Positive value Signup and view all the answers

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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Description

Test your knowledge on the processes of photosynthesis, physical and chemical changes, as well as exothermic reactions. This quiz will help you understand how these phenomena play a crucial role in the natural world. Are you ready to explore the science behind these important concepts?