Chemistry 04.01 Conservation of Mass

Examine the equation below. Explain what the subscripts of the reactants and products represent. AB(s) + C(l) → A(g) + BC(aq)

(s), (l), (g) - phase of each substance (aq) - compounds that have been dissolved in water to form a solution

Explain how the equation that makes water in the video represents a "balanced" equation.

2H2 plus O2 yields 2H2O The number 2 in front of the joined hydrogen atoms on the reactant side of this equation shows how many of these joint diatomic molecules are necessary for the chemical reaction to take place.

How do balanced equations demonstrate the conservation of mass?

Because matter cannot be created or destroyed in a chemical reaction, the mass of all the reactants will always add up to the total mass of all the products.

How are changes of state different from chemical change?

Changes of state, for example, from a solid to a liquid or from a liquid to a gas, always involve a physical change rather than a chemical one.

What happens to the chemical formula if you change a subscript instead of a coefficient?

Changing the subscripts in a formula changes the identity of the compounds.

What is a chemical equation, and how do scientists use these equations to represent chemical reactions?

Chemical equation: a representation, using formulas and symbols, of a chemical reaction Chemical equations allow us to describe the chemical reaction without having to write a long paragraph about the ratios of reactants and products in the reaction.

How does the law of conservation of mass also apply to physical changes?

The law of conservation of mass also applies to physical changes. For example, if you melt 150 grams of ice, you will get 150 grams of water—no more, no less.

In trial 1 of the vinegar-baking soda reaction, how did the masses of reactants and products compare?

The reactant's mass was bigger than the product's mass

How do chemists use coefficients to satisfy the law of conservation of mass?

They add coefficients to reactants and products in a chemical equation until there is the same number of each kind of atom on both sides of the equation.

Why was the result different in trial 2 compared to trial 1?

This is because all of the original atoms are still present from the beginning of the reaction; they have just been rearranged to bond in different ways.

Did this reaction demonstrate the law of conservation of mass? Explain why or why not.

Yes (In a closed (or sealed) system, the total mass of reactants and products will remain the same.)

Identify the number of atoms of each element in the reactants and the products in the following equation. CH4(g)+ O2(g) → CO2(g) + H2O(g)

carbon (C) 1 1 oxygen (O) 2 3 hydrogen (H) 4 2

In a chemical reaction, atoms cannot be _______ or _________, just rearranged.

created, destroyed

A chemical reaction starts with a ______ and ends with a ______.

reactant, product

How does a balanced chemical equation demonstrate conservation of mass?

shows equal ratios of compounds in the reactants and the products

Describe the law of conservation of mass.

the law that explains that mass cannot be created or destroyed within a closed system

What do coefficients in a chemical reaction indicate?

the number of molecules or formula units that take part in the chemical reaction

In trial 2 of the vinegar-baking soda reaction, how did the masses of reactants and products compare?

they are exactly the same

What factors are necessary for a chemical change to take place?

two or more elements or chemical compounds come into contact with one another when there is enough energy present