Lesson 4 Chemical Reactions and Energy

Unit 3 Elements, Compounds, and Reactions

ESSENTIAL QUESTION:

Why Do Chemical Reactions Always Involve A Change In Energy? P. 160

Vocabulary:Exothermic reactionEndothermic reactionRate of reactioncatalyst

What are exothermic reactions?

In chemical reactions, energy is either absorbed or release.

In a chemical reaction the chemical bonds in the reactants break and new chemical bonds are formed.

When chemical bonds breaks, the bond releases chemical energy.

When a chemical bond forms, chemical energy is absorbed.

What are exothermic reactions?

An Exothermic Reaction Is A Chemical Reaction That Releases Energy By Light Or Heat. It Is The Opposite Of An Endothermic Reaction.

Expressed In A Chemical Equation: Reactants → Products + Energy.

Signs that an exothermic reaction has taken place include heat, fire, electricity, light, sound, or thermal energy.

WHAT ARE ENDOTHERMIC REACTIONS?

A chemical reaction accompanied by the absorption of heat is an endothermic reaction.

Reactants + energy products.Endothermic reactions can absorb several types of

energyPhotosynthesis is an example of an endothermic

reaction where plants absorb light energy from the sun.

PHOTOSYNTHESIS EQUATION

COMPARING/CONTRASTING REACTIONS

What can affect the rate of a chemical reaction?

The rate of the reaction is the speed at which a reaction occurs.

Factors that influence the reaction rates of chemical reactions include the concentration of reactants, temperature, the physical state of reactants and their break-up of pieces (dispersion), the solvent, and the presence of a catalyst.

Demonstration of exposed surface area.

What are catalysts?

A catalyst is a substance that speeds up a chemical reaction.

A reaction using a catalyst will not produce more product; it will produce the same amount of product faster.

The best example of effective catalyst is enzymes that speed up reactions in the human body needed for your cells to work properly.

Enzymes as a catalyst

Videos

https://study.com/academy/lesson/endothermic-and-exothermic-reactions.html

http://study.com/academy/lesson/effect-of-catalysts-on-rates-of-reaction.html

Something to think about;

1. How can you identify the type of reaction that is occurring simply by absorbing the reaction?

2. How do photosynthesis and human cells processes work together to benefit people?

HOMEWORK

Complete Lesson 4 Review page 167.Write vocabulary and definitions on page 160Complete worksheets – word puzzle and valence

electrons.For Thursday, December 10, (A-Day) or Friday,

December 11, (B-Day) complete biography folderQuiz/Exam Review: Unit 1 Lesson 3 vocabulary and

Unit 2 lesson 1 vocabulary.