Chemistry Chapter on Activation Energy

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Questions and Answers

What is activation energy?

Activation energy is the minimum amount of energy needed to start a chemical reaction.

What role does activation energy play in chemical reactions?

Activation energy is the energy absorbed before it can start a chemical reaction.

What generalization can be made about activation energy in exothermic and endothermic reactions?

The diagram shows the amount of energy the reaction starts with and how much energy is being released or absorbed depending on the reaction that is occurring.

Which would react more quickly in a chemical reaction: a single sugar cube or an equal mass of sugar crystals? Explain.

The sugar crystals would react more quickly because they have a greater surface area facilitating faster reactions. Signup and view all the answers

What are four ways that chemists can control the rates of chemical reactions?

Surface area, temperature, concentration, catalysts, and inhibitors. Signup and view all the answers

Why can the rock at the top of the hill not roll down?

The rock cannot roll down until a small push gets it going. Signup and view all the answers

What happens when chemical reactions get a push?

A reaction won't begin until the reactants have enough energy to push them 'over the hump.' Signup and view all the answers

What do chemical reactions need to get started?

All chemical reactions need a certain amount of activation energy to get started. Signup and view all the answers

What happens if you mix two gases together?

They can remain unchanged for years until a tiny amount of activation energy is provided. Signup and view all the answers

What are exothermic reactions?

The burning of fuel, such as wood, natural gas, or oil. Signup and view all the answers

What do most endothermic reactions require and what are some examples?

Most require a continuous source of heat; for example, baking bread requires added heat until the process is complete. Signup and view all the answers

What do both endothermic and exothermic reactions need?

Both need energy to get started. Signup and view all the answers

What are the rates for chemical reactions?

Chemical reactions vary in rate; some, like explosions, are very fast, while others, like rusting, are slower. Signup and view all the answers

Chemists can control rates of reactions by changing what factors?

Changing factors such as surface area, temperature, concentration, and using catalysts and inhibitors. Signup and view all the answers

What do solid substances do in reactions with liquids or gases?

Only the particles on the surface come into contact with the other reactant. Signup and view all the answers

What can grain dust prevent?

Grain dust reacts explosively with oxygen, so minimizing it helps prevent accidents. Signup and view all the answers

What two ways do faster moving particles increase the reaction rate?

Faster moving particles come into contact more often and have more energy to overcome the activation energy 'hump.' Signup and view all the answers

What slows down reaction rates?

Reducing temperature slows down reaction rates. Signup and view all the answers

What is the third way to increase the rate of chemical reactions?

The third way is to increase the concentration of the reactants. Signup and view all the answers

What is an example of concentration in a chemical reaction?

Adding a larger spoonful of sugar makes lemonade sweeter. Signup and view all the answers

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Study Notes

Activation Energy

Minimum energy required to initiate a chemical reaction.
Essential for reactants to overcome energy barriers to transform into products.

Role in Chemical Reactions

Activation energy must be absorbed for a reaction to commence.
It acts as the initial energy input to break chemical bonds.

Exothermic vs. Endothermic Reactions

Exothermic reactions release energy, while endothermic reactions absorb energy.
A diagram illustrates energy levels before and after reactions, highlighting energy changes.

Reaction Rates of Different Substances

Sugar crystals react faster than a solid sugar cube due to greater surface area exposure.
More surface area facilitates quicker interactions with reactants.

Controlling Reaction Rates

Chemists can manipulate reaction rates through various factors: temperature, concentration, surface area, and catalysts/inhibitors.

Energy Requirement Analogy

Chemical reactions are likened to a rock needing a push to roll down; activation energy is necessary to initiate the process.

Mixing Gases

Two mixed gases may remain unchanged until activation energy, such as a spark, triggers a reaction.
Initial reactions provide energy for further reactions to occur rapidly.

Specific Examples of Reactions

Exothermic reactions: burning fuel (wood, gas, oil).
Endothermic reactions need continuous heat, exemplified by baking bread.

Variability in Reaction Rates

Chemical reactions vary in speed: rapid (explosions) vs. slow (rusting).
Variables such as temperature or concentration can change a reaction's rate.

Size and Surface Area Influence

Solid particles react only at their surface; breaking solids into smaller pieces increases the surface area and accelerates reaction rates, though it may pose risks.

Grain Dust Hazard

Grain dust can lead to explosive reactions with oxygen; controlling dust in grain elevators is crucial for safety.

Effects of Temperature on Reaction Rates

Higher temperatures generally increase reaction rates due to more frequent particle collisions and higher kinetic energy.

Concentration Impact

Increasing reactant concentration enhances reaction rates, creating more interaction opportunities.
Example: Doubling sugar in lemonade significantly elevates sweetness, illustrating the effect of concentration on taste perception.