Vocabulary
This is the smallest particle of an element that still has the properties of that element.
Atom
In H2O, how many hydrogen atoms are present in one molecule
2, Two Atoms
State the Law of Conservation of Mass in one sentence
Mass/Matter cannot be created nor destroyed, it simply changes forms
Is a sealed container an example of an open or closed system for a chemical reaction? Explain briefly.
Closed because the container is SEALED
True or False: Atoms can turn into a different element during a normal chemical reaction.
False
The name for the new substances formed during a chemical reaction (found to the right of the arrow)
Product
For the molecule CO2, how many oxygen atoms are present in two molecules of CO2?
Four, Four Atoms
If a closed reaction starts with 10 g of reactant A and 15 g of reactant B, what should be the mass of products (assuming no mass lost or gained)?
10+15 = 25 Grams
Give one example of an open system in a classroom chemistry demonstration.
An open beaker where gas can escape during a reaction (e.g., vinegar and baking soda in an open flask)
True or False: When a solid dissolves in water, the mass of the water-plus-dissolved-solid system changes because the solid disappears
False
small number attached to only one element in a compound and depicts that number of atoms for that element alone.
Subscript
How many total atoms are in one molecule of NaCl?
2 - 1 Na, 1 Cl
A student measures 25.0 g of a sealed reaction mixture before reaction and 25.0 g after reaction. What does this show about the atoms and mass?
The atoms and mass stay the same; mass is conserved
A student places 10 g of vinegar and 10 g of baking soda into a sealed plastic bag. The substances react and produce bubbles. After the reaction stops, the student measures the mass of the sealed bag and its contents.
Which statement best predicts the mass after the reaction?
A. The mass will be less than 20 g because some matter was used during the reaction.
B. The mass will be greater than 20 g because a new substance formed.
C. The mass will remain 20 g because the atoms were rearranged into new substances.
D. The mass will be 10 g because the baking soda was used up.
C. The mass will remain 20 g because the atoms were rearranged into new substances.
A student says "Mass always decreases in chemical reactions because energy is released." Explain why this statement is incorrect for typical chemical reactions
Incorrect because chemical reactions rearrange atoms; the mass of atoms remains; energy release does not remove mass in ordinary chemical reactions to a measurable extent
The substance(s) present at the start of a chemical reaction. (found on the left side of the arrow)
Reactants
In the formula 2H2 + O2 → 2H2O, how many oxygen atoms are on the reactant side and how many on the product side?
Reactants: 2
Products: 2
Explain one reason why measured mass might appear to change during a reaction even when the Law of Conservation of Mass holds
Some material may have escaped (like a gas), or some spilled, or measurement error
Two groups conduct the same chemical reaction.
Both groups begin with 50 g of reactants. Group A measures 44 g after the reaction, while Group B measures 50 g.
Which explanation best accounts for the results?
A. Group A's reaction destroyed 6 g of atoms.
B. Group B created 6 g of new atoms.
C. Some matter, such as a gas, escaped from Group A's container.
D. The atoms in Group A changed into atoms with less mass.
C. Some matter, such as a gas, escaped from Group A's container.
Explain why cutting an apple into pieces does not change the total mass of the apple (assuming no pieces are lost)
Cutting changes shape and size but not the number of atoms; if no pieces are lost, total mass is unchanged
The large number in front of a chemical compound and controls the total number of the atoms for every element that is behind it.
Coefficient
Given the equation C3H8 + 5O2 → 3CO2 + 4H2O, count the total number of hydrogen atoms before and after the reaction.
Reactants: 8 Hydrogens
Products: 8 Hydrogens
A chemical reaction occurs in a sealed container. Which TWO statements describe what happens to the atoms during the reaction?
☐ A. Some atoms disappear when new substances form.
☐ B. The atoms are rearranged into new combinations.
☐ C. Atoms change into completely different types of atoms.
☐ D. The total number of each type of atom remains the same.
☐ E. New atoms are created when the reaction produces a gas.
B. The atoms are rearranged into new combinations. + D. The total number of each type of atom remains the same.
A student conducts a reaction in an open container. The student records:
Reactants = 62 g
Products = 55 g
The student says:
Which additional investigation would best help the student understand the result?
A. Repeat the reaction using a larger amount of reactants.
B. Repeat the reaction using a sealed container and measure the total mass.
C. Repeat the reaction and remove the products before measuring.
D. Repeat the reaction with a different color of container.
B. Repeat the reaction using a sealed container and measure the total mass.
A class performs a reaction that produces a gas and they notice the mass of the flask decreased. The student claims the Law of Conservation of Mass is false. Is the student correct?
The student is incorrect because the reaction produced a gas that simply escaped from the open flask, thus the Law of Conservation of Mass is still correct because the lost mass was not destroyed.