Chemical Reactions Ms. Haut Biology Engineering 2.
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Transcript of Chemical Reactions Ms. Haut Biology Engineering 2.
Chemical Reactions
• Reactants—starting material
• Products—ending material
• Chemical Equation
Reactants → Products
Chemical Reactions• Occur when bonds
between the outermost parts of atoms are formed or broken
• Involve changes in matter, the making of new materials with new properties, and energy changes
Chemical Equations
• Show the kind of reactants and products and their relative amounts in the reaction
4 Al + 3 O2 → 2 Al2O3
Chemical Equations• Because of the Because of the
principle of the principle of the conservation of conservation of mattermatter, ,
• an an equation must equation must be balanced.be balanced.
• It must have the same It must have the same number of atoms of number of atoms of the same kind on both the same kind on both sidessides
Balancing Chemical Equations
• You may add coefficients in front of the compounds to balance the reaction, but you may notnot change the subscripts.
3 CO2
• Changing subscripts changes the compound.
Subscripts vs. CoefficientsSubscripts vs. Coefficients• Subscripts tell you Subscripts tell you
how many atoms of a how many atoms of a particular element are particular element are in a compound. in a compound.
• The coefficient tells The coefficient tells you about the you about the quantity, or number, quantity, or number, of molecules of the of molecules of the compound.compound.
4 Al + 3 O2 → 2 Al2O3
This equation means4 Al atoms + 3 O2 molecules →produces→ 2 molecules of Al2O3
Four basic steps to balancing a chemical equation.• Write the correct formula for the reactants and the products in
an unbalanced equation.• Inventory the number of each kind of atom on both sides of the
unbalanced equation.• Determine where to place coefficients in front of formulas to
balance the equation.• Take another inventory to determine if:
– The numbers of atoms on both sides of the equation are now balanced.
– The coefficients are in the lowest possible whole number ratios.
Write and balance the chemical equation for:
methane reacting with oxygen gas to produce carbon dioxide and water
1) What are the formulas of the reactants and products?
REACTANT PRODUCT
Methane: CH4 Carbon dioxide: CO2
Oxygen gas: O2 Water: H2O
2) Write the general formula of the reaction
CH4 + O2 CO2 + H2O
Let’s Practice…
CH4(l) + O2(g) CO2 (g) + H2O(l)
Count the number of same elements on both sides
ELEMENT REACTANT PRODUCT
C 1 1
H 4 2
O 2 3
C is balanced by H and O are not…H is off by 2 and O is off by 1
CH4 + O2 CO2 + H2O
C is balanced but H and O are not…H is off by 2 and O is off by 1
For H: What number do you multiply the 2 H on the product byto get 4H? 2
CH4 + O2 CO2 + 2 H2O
So now there are 4 H’s on both sidesNow there are 2 O on the reactant side and 4 O on the product side
For O: what number do you multiply the 2O on the reactantside to get 4O? 2
CH4 + 2 O2 CO2 + 2 H2O