balancing equations - wordpress.com

Balancing Equations

17/05/2016 ©cgrahamphysics.com 2016

Let’s bake a cake • What ingredients do you need? Be as specific as possible

1 (18.25-ounce) box white cake mix) 1 large orange, zested, about 1/4 cup 1 1/3 cups no pulp orange juice 3 egg whites 2 tablespoons vegetable oil Frosting: 1/2 stick (4 tablespoons) unsalted butter, at room temperature 1/3 cup creme fraiche 1 pound powdered sugar 1/4 cup raspberry jam Water, as needed 1/4 cup raspberry jam 1 (6-ounce) container fresh raspberries

Cake3 tablespoons unsalted butter, melted and cooled, plus more for buttering cake pan 1/2 cup (2 1/2 ounces) unbleached all-purpose flour plus more for dusting cake pan 1/4 cup Dutch-process cocoa 6 large eggs, at room temperature 3/4 cup (4 3/4 ounces) superfine sugar 1 teaspoon vanilla extract Syrup1/2 cup sugar, 1 ounce (2 tablespoons) kirsch Assembly4 cups heavy cream 1 cup (4 ounces) powdered sugar 2 teaspoons vanilla extract 2 cups Spirited Sour Cherries , 8 fresh cherries with stems (optional) About 2 1/2 ounces dark chocolate (at least 60% cacao) in a single block About 1/2 cup ground dark chocolate (at least 60% cacao) or chocolate cookie crumbs Powdered sugar for dusting


http://www.epicurious.com/recipes/food/views/51125800

Starter

• Which of these substances are elements?

• What are the others called?


Aim

• Balance chemical symbol equations

Key words

• Compounds

• Chemical formula


Have you ever wondered?

The bigger picture

How do chemists know how to combine chemicals in the right way?


100g g melting

100

Let’s start by looking at food to learn how to write chemical formulae

• It has changed state from solid to liquid. • No chemical reaction has taken place.


100g + 50g g 150

Let’s add Smarties to the chocolate mix

• A new product (smocolate) has been formed. • A chemical reaction has taken place.


100g + 50g g 150

Let’s add Smarties to the chocolate mix

• Mass reactants = mass products • The law of conservation of mass 17/05/2016 ©cgrahamphysics.com 2016

200g + g 300 g 100

• Write a word equation for the production of smocolate: • Chocolate + Smarties Smocolate


Lets make up some formulae

Chocolate = Ch

Smarties = Sm

Smocolate =

What is the chemical formula for Smocolate?

ChSm 2

Each chunk of Smocolate has two Smarties on top, correct the formula.


ChSm2

ChSm2

The small number means there are 2 Smarties in the Smocolate molecule.

2

The big number means there are 2 Smocolate molecules


Ch + Sm ChSm2

Balance this equation so the REACTANTS add up to make the PRODUCT.

2


Now try these!

1. 2Ch + __Sm __ ChSm2

2. __Ch + 6Sm __ ChSm2

3. __Ch + __Sm 4ChSm2

4. 5Ch + __Sm __ ChSm2

4 2

3 3

4 8

10 5


Oh no! We can’t get normal Smarties any more. Only Supersmarties that

come in threes!


Spersmarties 𝑆𝑚3

Supersmarties

can be broken

apart to make

Smocolate, but we

can only buy them

stuck together.


Try making Smocolate with Supersmarties!

__Ch + 2Sm3 __ ChSm2

3 3


Now apply that to atoms.

carbon + oxygen carbon dioxide

C + O2 CO2

Does this equation balance?

Yes, there are the same number of each atom in the reactants and

products. 17/05/2016 ©cgrahamphysics.com 2016

Now apply that to atoms.

hydrogen + oxygen water

H2 + O2 H2O

Does this equation balance?

No, there is more oxygen in the reactants than the products.


hydrogen + oxygen carbon dioxide

__H2 + __O2 __H2O

Balance the equation

2 2


Balance this!

__N2 + __H2 __NH3

2 3


Plenary: MWB

• Draw an element

• Draw a mixture

• Draw a compound

• Draw a molecule

• List the diatomic molecules


Balance the equations

• 𝐶3𝐻8 +  𝑂2   𝐶𝑂2 +  𝐻2𝑂

• 𝐶4𝐻10 + 𝑂2    C  +  𝐻2𝑂

• 𝐶4𝐻10 +  𝑂2   CO +  𝐻2𝑂

• 𝐶4𝐻10 + 𝑂2   𝐶𝑂2  +  𝐻2𝑂

• 𝐶5𝐻12 +  𝑂2    𝐶𝑂2  +  𝐻2𝑂

• 𝐶6𝐻14 +  𝑂2   CO +  𝐻2𝑂

5 3 4

2 5 8 10

2 9 8 10

2 13 8 10

8 5 6

2 13 12 14


Key words

• Compounds – composed of two or more different elements

• Chemical formula - a set of chemical symbols showing the elements present in a compound and their relative proportions, and in some cases the structure of the compound


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