Unit 6 Section 1: Modeling Chemical Reactions

Unit 6 Section 1: Modeling Chemical Reactions

Lesson Objectives

• Describe what causes chemical reactions

• Write Balanced Equations for chemical reactions

• Explain what causes chemical reactions

​Introduction

• ​Chemical Reaction: The process by which one or more substances are changed into one or more different substances

  • ​Two components

    • ​Reactants: the original substances before the reaction takes place

      • Reactants must come together in order for a reaction to take place​

    • ​Products: the resulting substances after the reaction takes place

• ​According to the law of conservation of mass: the total mass of reactants must equal the total mass of the products

​Indications of a chemical reaction

• Two main categories:

  • Changes in Energy

    • Release of energy as heat and light: ​Usually shows a chemical reaction, but not always

    • Production of a sound​

​Indications of a chemical reaction

• Two main categories:

  • Formation of a new substance

    • ​Production of a gas

    • ​Formation of a precipitate

      • ​Precipitate: A solid substance that results from the mixing of two dissolved liquids

    • ​An odor change or A color change

      • Note: A color change only counts if it is not possible to revert to the original color of the reactants, otherwise it is a physical change

​Chemical Equations

• A Chemical Equation describes a chemical reaction by using

  • symbols and formulas

  • the relative molar amounts of both reactants and products

• A recipe for a reaction

  • Coefficients: Large numbers in front of the chemical formulas in a chemical equation

    • Tell the Number of Moles involved in the reaction

    • If no number, the number of moles is automatically one

• Example: Ammonium Dichromate Decomposition

Draw

Circle the reactants in the chemical reaction $$\left(NH_4\right)_2Cr_2O_{7\left(s\right)}\rightarrow N_2+Cr_2O_{3\left(s\right)}+4H_2O_{\left(g\right)}$$  

Draw

Underline the products in the chemical reaction $$\left(NH_4\right)_2Cr_2O_{7\left(s\right)}\rightarrow N_2+Cr_2O_{3\left(s\right)}+4H_2O_{\left(g\right)}$$  

Multiple Choice

How many Moles of water are involved in the decomposition of ammonium dichromate?

• 1

• 2

• 4

• 3

Multiple Choice

How many Moles of Nitrogen Gas are involved in the decomposition of ammonium dichromate?

• 1

• 2

• 4

• 3

​Characteristics of Chemical Equations

• ​​Required information

  • ​The equation must represent all known facts: all reactants and products must be known

  • ​The equation must contain the correct formulas for the reactants and products:

    • Make sure you keep track of diatomic molecules

  • ​The law of conservation of Mass must be satisfied: Atoms can not be created or destroyed, so the same number of each must appear on both sides of the equation

​Using Word Equations and Formula Equations

• ​When writing chemical equations it helps to first write everything out using words instead of symbols

  • ​This only gives you a qualitative description, because no amounts are given

  • ​Example: Here is the word equation for the reaction of methane and oxygen 

• ​Once you have written everything using words, you can replace the words with the appropriate chemical formulas and symbols to write a formula equation

  • What are our chemical formulas?

    • ​Methane: CH₄

    • ​Oxygen: is one of the diatomic molecules: O₂

    • ​Carbon Dioxide: CO₂

    • ​Water: H₂O

  • We can show the state of matter each part of the equation is in using the first letter of that state of matter

​

• ​Our equation shows what's involved but not how much because it's not Balanced

  • ​Let's look at our reactants and our products and count how many of each atom we have on both sides

  • ​We need to add coefficients to the products to balance out the equation

    • ​Let's start by looking at Hydrogen since it is in the least number of places in the products

Multiple Choice

How many more moles of hydrogen do we need on the products side of the equation to balance out the equation

• 1

• 2

• 3

• 4

• ​ ​The easiest way to balance our hydrogen is to add a 2 in front of the water

• ​Let's check our reactants and products again to see if it is balanced

  • ​Our equation is not balanced, so we need to add another coefficient, this time to the reactants

Multiple Choice

How many more moles of Oxygen do we need on the reactants side to have a balanced equation?

• 1

• 2

• 3

• 4

Balancing Equations Practice 1

• Balance the Equation: AgNO₃ + Cu → Cu(NO₃)₂ + Ag

  • Step 1: Identify what we have on each side of the equation

  • Step 2: Identify what we can balance first

    • In general, You should balance Oxygen and Hydrogen last, so we start with nitrogen

Dropdown

What number can we put in to balance the nitrogen in the following equation:

​

Select answer

AgNO₃ + Cu → Cu(NO₃)₂ + Ag

Balancing Equations Practice 1

• New Equation: 2 AgNO₃ + Cu → Cu(NO₃)₂ + Ag

  • Step 3: Check both sides of the equation for balance

  • Step 4: Fix any unbalanced parts of the equation

Dropdown

What number can we put in to balance the silver in the following equation:

​ 2 AgNO₃ + Cu → Cu(NO₃)₂ + ​

Select answer

Ag

Balancing Equations Practice 2

• Balance the following equation:

• In this equation, we have polyatomic ions that can be treated as one unit because they are on both sides of the equation.

• Step 1: Determine how many of each atom/polyatomic ion there are on each side of the equation.

Multiple Choice

How many ammonium (NH₄) ions are in the reactants?

• 1

• 2

• 3

• 4

Multiple Choice

How many ammonium (NH₄) ions are in the products?

• 1

• 2

• 3

• 4

Multiple Choice

How many Sulfate(SO₄) ions are in the Reactants?

• 1

• 2

• 3

• 4

Multiple Choice

How many Sulfate(SO₄) ions are in the products?

• 1

• 2

• 3

• 4

Multiple Choice

How many Hydrogen atoms are in the reactants?

• 1

• 2

• 3

• 4

Multiple Choice

How many Oxygen atoms are in the reactants and not in the sulfate ion?

• 1

• 2

• 3

• 4

Multiple Choice

How many Oxygen atoms are in the products and not in the sulfate ion?

• 1

• 2

• 3

• 4

Balancing Equations Practice 2

• Balance the following equation:

• Step 2: Start balancing your atoms/ions

  • In general, we do Oxygen and Hydrogen last, so we will start by balancing the Ammonium

Drag and Drop

Balance the Ammonium in this equation:​

Placeholder

NH₄ +​ H₂SO₄ --> (NH₄)₂ + H₂O

Drag these tiles and drop them in the correct blank above

2

1

3

4

Balancing Equations Practice 2

• Balance the following equation:

• Step 3: Update the number of atoms/ions we have on both sides of the equation

• Step 4: Now we need to balance our oxygen and hydrogen

  • We need more on the products side, so we will add a coefficient to the water

Drag and Drop

Balance the Water in the Following Equation: 2 NH₄OH +H₂SO₄ --> (NH₄)SO₄ +​

Placeholder

H₂O

Drag these tiles and drop them in the correct blank above

2

1

3

4

Balancing Equations Practice 2

• Balance the following equation:

• Step 5: Update the number of atoms/ions we have on both sides of the equation

• Step 6: Double-check your work

Balancing Equations Practice 3

• Solid aluminum carbide, Al₄C₃, reacts with water to produce methane gas and solid aluminum hydroxide. Write a balanced chemical equation for this reaction.

• Step 1: Identify how many of each atom we have on each side of the Equation

Categorize

Options (8)

4 Aluminun

1 Aluminum

3 Carbon

1 Carbon

2 Hydrogen

1 Oxygen

7 Hydrogen

3 Oxygen

Organize these options into the right categories

Reactants

Products

Balancing Equations Practice 3

• Solid aluminum carbide, Al₄C₃, reacts with water to produce methane gas and solid aluminum hydroxide. Write a balanced chemical equation for this reaction.

• Step 2: Begin Balancing the equation with either the Aluminum or the Carbon Atoms

  • DO NOT TRY TO DO BOTH AT THE SAME TIME

    • Let's do Aluminum

Drag and Drop

Fill in the blank to balance Aluminum on both sides of the equation: Al₄C₃+H₂O-->CH₄+​

Placeholder

Al(OH)₃

Drag these tiles and drop them in the correct blank above

4

2

6

8

Balancing Equations Practice 3

• Solid aluminum carbide, Al₄C₃, reacts with water to produce methane gas and solid aluminum hydroxide. Write a balanced chemical equation for this reaction.

• Step 3: Update how many of each atom you have on both sides of the equation

• Step 4: Now balance the Carbon

Drag and Drop

Fill in the blank to balance Carbon on both sides of the equation: Al₄C₃+H₂O-->​

Placeholder

CH₄+​ 4 Al(OH)₃

Drag these tiles and drop them in the correct blank above

2

6

8

3

4

Balancing Equations Practice 3

• Solid aluminum carbide, Al₄C₃, reacts with water to produce methane gas and solid aluminum hydroxide. Write a balanced chemical equation for this reaction.

• Step 5: Update how many of each atom you have on both sides of the equation

• Step 6: Now we will choose between Oxygen and hydrogen to Balance

  • We should do Oxygen because it only appears in one spot on both sides of the equation

Drag and Drop

Fill in the blank to balance Oxygen on both sides of the equation: Al₄C₃+ ​

Placeholder

H₂O-->​ 3 CH₄+​ 4 Al(OH)₃

Drag these tiles and drop them in the correct blank above

2

6

8

4

12

10

Balancing Equations Practice 3

• Solid aluminum carbide, Al₄C₃, reacts with water to produce methane gas and solid aluminum hydroxide. Write a balanced chemical equation for this reaction.

• Step 6: Double-check your equation and see if it is balanced

Multiple Select

What two Categories indicate that a chemical reaction has taken place?

• Changes in energy

• Formation of a new Substance

• Changes in state of matter

• There is no way to tell if a chemical reaction has taken place

Multiple Choice

Coal contains carbon and other elements. Carbon dioxide forms when coal burns in the presence of oxygen. Which of these statements is the best evidence that a chemical reaction occurs when coal burns?

• The shape of the coal changes
• Oxygen is present
• A new substance is produced
• Coal is made up of more than one element

Multiple Choice

In a chemical equation, is it true that -

• the reactant side and product side can have different numbers of atoms for each element
• there can be different elements on the reactant side and the product side
• an element or compound must be accompanied by a phase change
• the coefficients indicate the number of molecules of each reactant used and the number of molecules of each product made

Multiple Choice

True or False: In a chemical reaction, no new atoms are created, and no atoms are destroyed. 

• true
• false

Multiple Choice

If reaction starts with 20g of reactants it should produce... 

• a total of 40g of product
• a total of 10g of product
• a total of 80 g of product
• a total of 20g of product

Multiple Choice

Is the following equation balanced: 4Fe + 3O₂ --> 2Fe₂O₃

• Yes

• No

Multiple Choice

True or False: The reactants are on the left side of the chemical equation.

• True
• False

Match

Match the following symbol to their meaning in a chemical reaction

• (s)

• Δ

• →

• (aq)

• ↔

Solid

A change

Yields

Aqueous

Reversible Reaction

• Solid

• A change

• Yields

• Aqueous

• Reversible Reaction