Chemical Reactions
Burning wood leaves behind less mass. Why?
Some of the products of the reaction were released as gas.
How many hydrogen atoms are in 3NaOH + H₃PO₄?
6
A chemical formula shows the types of atoms and the number of each in a compound. What does H₂O tell you?
It contains two hydrogen atoms and one oxygen atom.
What does a chemical equation show about a reaction?
It shows the reactants, products, and how atoms are rearranged.
What does a chemical model represent in a reaction?
It shows how atoms are rearranged to form new substances.
Ethane reacts with oxygen. Look at the chemical equation and describe the atoms in the products:
2C2H6 + 7O2 → 4CO2 + 6H2O
4 atoms of C (carbon)
14 atoms of O (oxygen)
12 atoms of H (hydrogen)
How many phosphorus atoms are in Na₃PO₄?
1
What does the subscript in a chemical formula indicate?
The number of atoms of that element in the molecule.
Why must a chemical equation be balanced?
To show that the same number of each type of atom exists before and after the reaction.
Why are models useful when studying chemical reactions?
They help visualize how atoms move and bond during a reaction.
Coal reacts with oxygen to form sulfur dioxide and sulfur trioxide.
They have different chemical properties than the reactants.
How many oxygen atoms are in 3H₂O?
3
How many total atoms are in one molecule of C₆H₁₂O₆?
24 atoms
In the equation 2H₂ + O₂ → 2H₂O, how many oxygen atoms are on each side?
Two oxygen atoms.
In a model of 2H₂ + O₂ → 2H₂O, how many hydrogen atoms are in the reactants?
Four hydrogen atoms.
Complete the balanced equation: 4Fe + 3O₂ → ___Fe₂O₃
2
How many atoms of each element are in the products of Pb(NO₃)₂ + 2NaI?
Pb: 1, I: 2, Na: 2, N: 2, O: 6.
Why do different compounds have different chemical formulas?
Because they are made of different types and numbers of atoms.
What does the coefficient in a chemical equation tell you?
How many molecules or units of each substance are involved in the reaction.
What does it mean if a model shows the same number of each atom before and after a reaction?
The reaction follows the law of conservation of mass.
Sodium and chlorine react to form sodium chloride. Why does the product have different properties?
It’s a new compound with a different chemical structure.
How is matter conserved in a chemical reaction?
The number of atoms of each element remains the same before and after the reaction.
How can you tell that NaCl and H₂O are different substances just by looking at their formulas?
They contain different elements in different ratios, which means they have different properties.
How can you tell that a chemical reaction follows the law of conservation of mass?
The total number of atoms of each element is the same on both sides of the equation.
How can you tell if a chemical model is balanced?
Each type of atom appears in equal numbers on both sides of the reaction.