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Published byRoberta Andra Alexander Modified over 6 years ago
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Molecular rep of a rxn CH4 + O2 CO2 + H2O
Notice that there are 4 hydrogen atoms in the reactants and only 2 in the products. Notice that there are only 2 oxygen atoms in the reactants and 3 in the products
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Chemical Equation A representation of a balanced chemical reaction:
CH O2 CO H2O reactants products
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Molecular rep of a rxn CH O2 CO H2O
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Chemical Equation CH4 + 2O2 CO2 + 2H2O
The equation is balanced – there are the same number of each atom on each side of the arrow. 1 molecule of methane reacts with 2 molecules of oxygen To produce: 1 molecule of carbon dioxide and 2 molecules of water
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To Balance Equations Start with the element that is most complex, usually Make sure the same numbers of atoms of that element are on both sides of the equation You CANNOT change the formula of a molecule in an equation You must change the COEFFICIENT of the molecule to make there be the same numbers
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Balance the Reaction 1 Ca + AlCl3 CaCl2 + Al
Chlorine is the most complex There are 3 Cl’s in the reactants and 2 Cl’s in the products The least common multiple between 3 and 2 is…6 In order to make 6 Cl’s on each side, put the coefficient 2 in front of the AlCl3 and the coefficient 3 in front of the CaCl2.
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Balance the Reaction 1 Ca + 2AlCl3 3CaCl2 + Al
Now you have changed the number of Aluminum’s in the reactants to 2. There is only 1 Al in the products In order to make there be 2 Al’s in the products, put the coefficient 2 in front of the Al You have also changed the number of Calcium’s in the products to 3. There is only 1 Ca in the reactants Put the coefficient 3 in front of the Ca.
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Balance the Reaction 1 3Ca + 2AlCl3 3CaCl2 + 2Al
Check to see that there are equal numbers of each atom on each side of the reaction… The reaction is Balanced!!
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Balance the Reaction 2 C2H5OH + O2 CO2 + H2O
Hydrogen is the most complex There are 6 H’s in the reactants and only 2 in the products In order to make 6 H’s in the products, put the coefficient 3 in front of the H2O
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Balance the Reaction 2 C2H5OH + O2 CO2 + 3H2O
Carbon is the next most complex There are 2 C’s in the reactants and only 1 in the products In order to make 2 C’s in the products, put the coefficient 2 in front of the CO2
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Balance the Reaction 2 C2H5OH + O2 2CO2 + 3H2O
Now you have changed the numbers of Oxygen atoms in the products – there are 7 O’s Changing the number of C2H5OH’s will force you to change the coefficients on the products One of the O’s is used up in the C2H5OH, so there are 6 O’s that need to be accounted for by the O2’s. Put the coefficient 3 in front of the O2 so there are 7 total O’s in the reactants.
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Balanced Reaction 2! C2H5OH + 3O2 2CO2 + 3H2O
Check to make sure that there are the same numbers of each atom on each side!
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Which of the following correctly balance the chemical equation given below?
CaO + C CaC2 + CO2 1. CaO2 + 3C CaC2 + CO2 2. 2CaO + 5C 2CaC2 + CO2 3. CaO + (2.5)C CaC2 + (0.5)CO2 4. 4CaO + 10C 4CaC2 + 2CO2
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Notice The number of atoms of each element must be the same on both sides of a balanced equation. Subscripts must not be changed to balance an equation. A balanced equation tells us the ratio of the number of molecules that react and are produced in a chemical reaction. Trial and error is a valid method to balance a chemical equation.
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Balance the following Reactions
N H2 NH3 H2O H O2 Mg + FeCl3 MgCl Fe Br FeCl3 FeBr Cl2
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Check your answers N2 + 3H2 2NH3 2H2O 2H2 + O2
3Mg + 2FeCl3 3MgCl2 + 2Fe 3Br2 + 2FeCl3 2FeBr3 + 3Cl2
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Balance the following reactions
NaCl + MgBr2 MgCl2 + NaBr Pb(NO3)2 + Na2SO4 NaNO3 + PbSO4 CH4 + O2 CO2 + H2O C4H10 + O2 CO2 + H2O
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Check Your Answers 2NaCl + MgBr2 MgCl2 + 2NaBr
Pb(NO3)2 + Na2SO4 2NaNO3 + PbSO4 CH4 + 2O2 CO2 + 2H2O C4H /2O2 4CO2 + 5H2O or 2C4H O2 8CO2 + 10H2O
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Balance the Reactions Al + O2 Al2O3 C3H8 + O2 CO2 + H2O
LiCl + CuSO4 CuCl2 + Li2SO4 NaCl + F2 NaF + Cl2
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Check Your Answers 4Al + 3O2 2Al2O3 C3H8 + 5O2 3CO2 + 4H2O
2LiCl + CuSO4 CuCl2 + Li2SO4 2NaCl + F2 2NaF + Cl2
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