Science: Chemical Reactions and Balancing Equations
Identify reaction evidence and balance simple chemical equations
Science: Chemical Reactions and Balancing Equations
Identify reaction evidence and balance simple chemical equations
Science - Grade 6-8
- 1
List two common signs that a chemical reaction may have occurred.
Think about what you might observe during a reaction in a lab.
Two common signs of a chemical reaction are a color change, gas production, temperature change, formation of a precipitate, or emission of light. Any two of these are acceptable examples. - 2
Explain why subscripts in a chemical formula should not be changed when balancing an equation.
Subscripts should not be changed because they are part of the chemical formula and show the number of atoms in each compound. Changing a subscript changes the substance itself instead of balancing the equation. - 3
Balance the equation: H2 + O2 -> H2O
Count oxygen atoms first, then adjust hydrogen if needed.
The balanced equation is 2H2 + O2 -> 2H2O. This gives 4 hydrogen atoms and 2 oxygen atoms on both sides of the equation. - 4
Balance the equation: N2 + H2 -> NH3
The balanced equation is N2 + 3H2 -> 2NH3. This gives 2 nitrogen atoms and 6 hydrogen atoms on both sides. - 5
Balance the equation: Na + Cl2 -> NaCl
Notice that chlorine is diatomic in Cl2.
The balanced equation is 2Na + Cl2 -> 2NaCl. This gives 2 sodium atoms and 2 chlorine atoms on both sides. - 6
Balance the equation: Mg + O2 -> MgO
The balanced equation is 2Mg + O2 -> 2MgO. This gives 2 magnesium atoms and 2 oxygen atoms on both sides. - 7
Balance the equation: Fe + O2 -> Fe2O3
Start by making the oxygen count even on both sides.
The balanced equation is 4Fe + 3O2 -> 2Fe2O3. This gives 4 iron atoms and 6 oxygen atoms on both sides. - 8
Balance the equation: Al + O2 -> Al2O3
The balanced equation is 4Al + 3O2 -> 2Al2O3. This gives 4 aluminum atoms and 6 oxygen atoms on both sides. - 9
Balance the equation: Ca + H2O -> Ca(OH)2 + H2
Treat the hydroxide group carefully and count all atoms on each side.
The balanced equation is Ca + 2H2O -> Ca(OH)2 + H2. This gives 1 calcium atom, 4 hydrogen atoms, and 2 oxygen atoms on both sides. - 10
Balance the equation: KClO3 -> KCl + O2
The balanced equation is 2KClO3 -> 2KCl + 3O2. This gives 2 potassium atoms, 2 chlorine atoms, and 6 oxygen atoms on both sides. - 11
Balance the equation: CH4 + O2 -> CO2 + H2O
Balance carbon first, then hydrogen, then oxygen last.
The balanced equation is CH4 + 2O2 -> CO2 + 2H2O. This gives 1 carbon atom, 4 hydrogen atoms, and 4 oxygen atoms on both sides. - 12
Balance the equation: C3H8 + O2 -> CO2 + H2O
The balanced equation is C3H8 + 5O2 -> 3CO2 + 4H2O. This gives 3 carbon atoms, 8 hydrogen atoms, and 10 oxygen atoms on both sides. - 13
A student says a balanced equation means the same number of molecules are on each side. Explain what is actually conserved in a balanced chemical equation.
Focus on atoms of each element.
A balanced chemical equation conserves the number of atoms of each element, not necessarily the number of molecules. Matter is conserved because atoms are rearranged into new substances without being created or destroyed. - 14
Balance the equation: Zn + HCl -> ZnCl2 + H2
The balanced equation is Zn + 2HCl -> ZnCl2 + H2. This gives 1 zinc atom, 2 hydrogen atoms, and 2 chlorine atoms on both sides. - 15
Balance the equation: AgNO3 + NaCl -> AgCl + NaNO3
Check whether the equation may already be balanced before changing coefficients.
The balanced equation is AgNO3 + NaCl -> AgCl + NaNO3. The equation is already balanced because each side has 1 silver atom, 1 sodium atom, 1 chlorine atom, 1 nitrogen atom, and 3 oxygen atoms.