Chemical Reactions - Chemical Changes and Conservation

Chemical Reactions - Chemical Changes

by S Harris

What standard are we working on?

​SPS3. Obtain, evaluate, and communicate information to support the Law of Conservation of Matter.

​

a. Plan and carry out investigations to generate evidence supporting the claim that mass is conserved during a chemical reaction. (Clarification statement: Limited to synthesis, decomposition, single replacement, and double replacement reactions.)

​

b. Develop and use a model of a chemical equation to illustrate how the total number of atoms is conserved during a chemical reaction. (Clarification statement: Limited to chemical equations that include binary ionic and covalent compounds and will not include equations containing polyatomic ions.)

​Learning Target

• ​I know...

  • ​how to identify reactants and products in a chemical equation.

Success Criteria

• ​I can...

  • determine the missing amount of a product or reactant using the law of conservation of mass.

What are everyday reactions

​Reactions include:

1. ​emotional responses

2. ​verbal responses

3. ​behavioral responses

Reactions are a change in our behavior based on the action of something else.​

English definition:

​- a response or change in a person as a result of a situation or stimulus

​Examples

​What does this have to do with physical science?

• ​ What is a chemical reaction?

  • ​a process in which one or more substances get converted (changed) into one or more new (different) substances

  • ​Chemical reactions take place all around us. EVERYDAY.

    • ​Examples include:

      • baking a cake

      • ​photosynthesis

      • ​the rusting of metal

      • burning wood

​What are the parts of a chemical reaction?

(Reactants)

(Products)

​Reactants are the starting material that will react

• these are ​written on the left side of the arrow

Products are the new substances produced after the reaction

• these are ​written on the right side of the arrow

A + B

C + D

Multiple Choice

Which of the following is a reactant from the following chemical equation?

CH₄ + O₂ ---> CO₂ + H₂O

• H₂O

• O₂

• CO₂

Multiple Choice

Which of the following is a product of the following chemical equation?

CH₄ + O₂ ---> CO₂ + H₂O

• H₂O

• O₂

• CH₄

​How do we know when a reaction has taken place?

​There are a few indicators for a chemical rxn:

• ​changes in ​color and temperature

• ​ production of gas

  • ​ex: bubbles

• ​formation of a precipitate

• ​production of light or sound

  • ​energy

​Answer: We look for indicators

• (evidence of change)

​What is the Production of Gas?

The formation of gas is a result of combining substances

• ​Examples:

  • ​bubbling

  • ​fizzing

  • ​foaming

​Formation of a Precipitate

Precipitates are solids that are produced as a result of a reaction in solution. It separates from the solution.

​

​Color Change

Color change is an indication of substances that have been mixed and have produced a different color from the original substances.

​

​Change in temperature

Is felt after the substances are mixed. You will know the temperature has changed because the surrounding area will become cooler or hotter than the original temperature.

​

​Production of Light or Sound

This is when energy gets released by matter. You may see a flash of light or hear a sound such as a "pop" or "bark"

​

​Antoine Lavoisier

French chemist who studied chemical rxns using scientific methods.

• ​Developed the Law of Conservation of Mass

​What is the Law of Conservation of Mass?

• Law that states...

  • ​In a chemical reaction (rxn), matter is not created nor destroyed, but is converted (transformed)

    • ​that the total mass of the products must always equal the total mass of the reactants

In other words....

​the amount you start with is the amount you end with

​The total mass of the products must always equal the total mass of the reactants.

​

Atoms cannot be created or destroyed in a reaction, they can only be rearranged

​​

This can be useful for determining the amount (mass or number of atoms) of a missing reactant or product​​

​What is the Law of Conservation of Mass?

Multiple Choice

The law of conservation states that the mass of the reactants is _______ the mass of the products.

• greater than

• less than

• equal to

Multiple Choice

If 14 grams of Aluminum (Al) and 23 grams of Oxygen (O) are mixed, what will be the total mass of the end product (Aluminum oxide)?

• 23 grams

• 14 grams

• 37 grams

• 40 grams