Chemical Reactions

Chemical Reactions

Fill in the Blank

According to the law of conservation of mass, matter cannot be created or ________

Multiple Choice

Which of the following is NOT evidence that that a chemical reaction has occurred?

• produces light/heat
• production of a gas
• formation of a precipitate
• melting

Multiple Choice

Bases turn blue litmus paper red.

• True

• False

Multiple Choice

Which of the following is an example that includes evidence of a chemical reaction?

• A sample of zinc is placed in water and it settles to the bottom

• A solid block of ice is heated and it completely melts into a liquid.

• Sugar that is burned gives off an odor and turns brown and then black.

• A tomato is placed into a blender and chopped up into smaller pieces.

Multiple Choice

Which of the following is a base?

• baking soda in water

• orange juice

• vinegar

• lemonade

Multiple Choice

Hydrogen peroxide breaks down to form water and oxygen gas. Which observation is evidence that a chemical reaction has occurred?

• The mass of the solution remains the same.
•  Phase changes are observed.
•  The color of the solution remains clear.
• The temperature of the solution increases. 

Multiple Choice

Which of the following pH values represents a base?

• 2.1

• 4.6

• 6.8

• 8.1

Multiple Choice

Which of the following examples shows that a chemical reaction has occurred?

• A rock breaks into smaller pieces when it is struck with a hammer.

• Rust forms on a hammer that has been left outside to long.

• A cup of water turns pink when a few drops of red food coloring are added.

• A solid is formed when heat is removed from a sample of water.

Multiple Choice

Which of the following is an acid?

• vinegar

• bleach

• sugar in water

• starch in water

• toothpaste in water

Multiple Choice

Which of the following IS a physical change?

• Getting a haircut
• Rusty metal
• sour milk
• A compound

Multiple Choice

Which of the following are properties of acids?

• They conduct electricity when dissolved in water

• They taste sour

• They react with metals to produce hydrogen gas

• All of the answer choices are correct

Multiple Choice

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

• A loss of transparency 
• An unexpected color change
• A temperature change
• The formation of a precipitate

Multiple Choice

When an acid is dissolved in water, it turns red litmus paper blue.

• True

• False

Multiple Choice

In a ___________change, a substance changes into a different substance.

• Physical

• Chemical

Multiple Choice

Milk is a very weak acid. What might its pH value be?

• 6.5

• 7.8

• 4.2

• 12.2

Open Ended

What is a Chemical Reaction?

Multiple Choice

Which of these pH values represent an acid?

• 4

• 8

• 10

• 12

A chemical reaction occurs when substances interact with each other . Bonds are broken and new ones are formed

Chemical Reactions results in Chemical change

Evidence of Chemical Change include

• Temperature Change

• Formation of Precipitate

• Color Change

• Formation of gases

What is the statement below saying?

2H₂ + O₂ = 2H₂O

Chemical Reactions are represented by Chemical Equation

Open Ended

What is an Equation?

• In Math an equation is a statement where both side are equal

• An equation is separated by an equal sign

• 5+5=10

• When we add 5 and 5 on the left side we get 10 which is the same on the right side

• Equation in Math deals with numbers and variables

• Chemical Equation deals with elements and compounds

• Numbers are sometimes placed below elements

• These numbers are called subscript .

• They tell how many atoms of the elements are present

• Numbers placed before an element or compound are called Coefficient

• A chemical Equation has reactants which are on the left side, products on the right and an arrow

• THe reactants are the substances which are interacting

• The Products are what are formed

• The Arrow shows the direction of Reaction

Multiple Choice

What is the number before a chemical formula called?

Ex: 2H₂ + O₂ --> 2H₂O

• Coefficient

• Subscript

• Atom

• Equation

Multiple Choice

What is the little number after an element in a chemical equation called.

Example: H₂

• Coefficient

• Subscript

• Atom

• Equation

Multiple Choice

What is the role of the arrow sign in a chemical reaction?

• Making sure atom counts on each side are the same.

• Separating products and reactants.

• Showing which substances were in the container first and which substances were added later.

• Showing which substances are solids and which are liquids or gases.

Multiple Choice

Identify the product(s) in the following chemical reaction:

Chromium oxide + Carbon → Chromium + Carbon monoxide

• Chromium and carbon.

• Chromium and carbon monoxide.

• Chromium and carbon dioxide.

• Chromium oxide and carbon.

Multiple Choice

Identify the reactants(s) in the following chemical reaction:

Chromium oxide + Carbon → Chromium + Carbon monoxide

• Chromium and carbon.

• Chromium and carbon monoxide.

• Chromium and carbon dioxide.

• Chromium oxide and carbon.

• The number of similiar elements on the left should always equal to those on the right

• After a chemical reactions that is not the case

• Example when a piece of paper is burned there is far less matter than what previously existed

• The matter is not lost it just changed formed

• The Law of Conservation of Matter state that Matter is neither created or destroyed, but just change in form

• For example a burning paper releases gases and water into a different form

• It is not destroyed just changed

Closed System

• In a closed system nothing is lost as all the atoms of an element at the beginning can be accounted for at the end because nothing escaped

Open System

• In an open system matter is allowed to escaped to its surrounding

• The number of atoms of each element on either side will be different

• This would not satisfy the Law of Conservation of Matter since it would appear that matter was lost

Multiple Choice

Are the number of atoms of each elements of the reactants the same as the products ?...

Al + O₂ --> Al₂O₃

• Yes!

• No!

Balancing Equations

• To satisfy the Law of Conservation of Matter equations are balanced

• To balance an Equation Coefficient are added

• Coefficient are used to multiply the subscript (number of atoms ) of each elements until both sides are equal

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How to Balance a Chemical Equation : 7 Steps (with Pictures) - Instructables

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Balance this equation

Li + Cl₂ -> LiCl

Balance this Equation

MgCl₂ --> Mg₄+ Cl₂

Multiple Choice

Balance this equation:

MgCl₂ --> Mg₄+ Cl₂

• It's already balanced.

• 4MgCl₂ --> Mg₄+ 4Cl₂

• 4MgCl₂ --> Mg₄+ 5Cl₂

Multiple Choice

Balance this equation:

2Li + Cl₂ -> LiCl

• 2Li + Cl₂ -> 4LiCl2

• 2Li + Cl₂ -> LiCl₂

• 2Li + Cl₂ -> 2LiCl

Multiple Choice

Is the following equation balanced or unbalanced ?

N₂ +3 H₂ --> 2NH₃

• Balanced

• Unbalanced

Multiple Choice

Is the following equation balanced or unbalanced ? 
Al + O₂ --> Al₂O₃

• Balanced
• Unbalanced

Multiple Choice

Which number should go in the blank?
_ H₂ + O₂ -> 2 H₂O

• 1
• 2
• 3
• 0

Multiple Choice

Which chemical equation best represents the Law of Conservation of Mass?

• H + O → H2O

• H2 + O2 → H2O

• 2H2 + O2 → 2H2O

• H2 + O2 → 2H2O2

Multiple Choice

Observe the reaction shown here. The formula for this equation is $$N_2\ +\ H_2\ \rightarrow\ NH_3$$  . Does this represent a balanced equation that obeys the Law of Conservation of Mass?

• No. The reactants and products are not equal in numbers of atoms of each element. 

• Yes. The reactants and products are equal in numbers of atoms of each element. 

Multiple Choice

Is this equation balanced?

• Yes

• No

Multiple Choice

Balancing this reaction: ____ CH₄ + ____ O₂ ---> ____ CO₂ + ____ H₂O

• 2,1,3,1
• 1,2,1,2
• 1,2,2,1
• 2,1,1,2

Multiple Choice

__NaClO₃ --> __NaCl + __O₂

• 2,2,2

• 2,2,3

• 3,2,2

• 1,2,3

Multiple Choice

__Na + __Cl₂ --> __NaCl

• 1,1,2

• 2,1,2

• 2,1,1

• already balanced

Types of Chemical Reaction

• Synthesis

• Decomposition

• Replacement

Synthesis

• Two or more elements joined together to become a compound

• 2Na + Cl₂ → 2NaCl

• 2NO + O₂ → 2NO₂

• 2 H₂O + O2 → 2 H₂O

Decomposition

A compound is broken down into individual elements

• H₂CO₃ → H₂O + CO₂

• 2 H₂O₂ → 2 H₂O + O2

• 2 H₂O → 2 H₂ + O₂

Single Replacement

One element replaces one element in a compound

• 2K + 2H2O → 2KOH + H2

• F₂ + 2NaCl → 2NaF + Cl₂

Combustion

Combustion is a type of chemical reaction where Oygen breaks down compounds

Multiple Choice

Which type of chemical reaction has two or more reactants to make one product?

• combustion

• single displacement

• double displacement

• synthesis

• decomposition

Multiple Choice

Combustion reactions will always involve

• Oxygen and a solid

• Liquid nitrogen and heat

• Oxygen and heat/energy

• CO and H₂O

Multiple Choice

What reaction has the following general formula:

AB --> A + B

• Combination

• Decomposition

• Single Replacement

• Double Replacement

• Combustion

Multiple Choice

Which type of chemical reaction has two or more reactants to make one product?

• combustion

• single displacement

• double displacement

• synthesis

• decomposition

Multiple Choice

At the end of chemical reactions, what is the total mass of the reactants compared to the total mass of the products?

• the product is doubled
• the product is half the mass of the reactants
• the mass is the same
• the mass changes depending on the reaction

Multiple Choice

In a chemical reaction, everything to the right of the arrow is called ______________.

• Products

• Yields

• Molecules

• Reactants

Multiple Choice

Which phrase describes what happens to atoms in a chemical reaction?

• never lost or gained, just rearranged

• sometimes lost, never rearranged

• sometimes lost, gained, or rearranged

• lost or gained, never rearranged

Multiple Choice

What reaction has the following general formula:

A + B --> AB

• Combination

• Decomposition

• Single Replacement

• Double Replacement

• Combustion