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2. Write word equations and skeleton equations for chemical reactions.
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11.1
Describing Chemical Reactions
On May 6, 1937, the huge airship
Hindenburg erupted into a fireball.
Within a short time, 210,000 cubic
meters of hydrogen had burned and
the airship was destroyed. The
chemical reaction that occurred is
“hydrogen combines with oxygen to
produce water.” You will learn to
represent this chemical reaction by a
chemical equation.
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© Copyright Pearson Prentice Hall
• Chemical reactions:
– The formations of new substances with properties different than the original substances
– Bonds are broken and reformed: matter is rearranged
– The law of conservation of mass applies: matter is not created or destroyed
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reactants → products
– Reactants are listed on left side of the arrow
– Arrow means “yields” or reacts to produce
– Products listed on right
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• Word equations: – names of reactants and products are given:
oxygen + glucose → water + carbon dioxide
water + carbon dioxide → oxygen + glucose
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11.1
Describing Chemical
Reactions
>
Writing Chemical Equations
Methane + Oxygen Æ Carbon dioxide + Water
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© Copyright Pearson Prentice Hall
11.1
Describing Chemical
Reactions
>
Writing Chemical Equations
iron + oxygen → iron(III) oxide
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© Copyright Pearson Prentice Hall
11.1
Describing Chemical
Reactions
>
Writing Chemical Equations
Hydrogen Peroxide Æ Water and Oxygen
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© Copyright Pearson Prentice Hall
• Write a word equation for the reaction. Na(s) + H2O(l) → NaOH(aq) + H2(g)
– Solid sodium reacts with water to form aqueous sodium hydroxide and hydrogen gas. Slide
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• Writing chemical equations – Formulas of reactants go on left of arrow, products on right
– Chemical formulas must be written correctly!
– A double arrow indicates a reversible reaction Slide
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11.1
Describing Chemical
Reactions
>
Writing Chemical Equations
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© Copyright Pearson Prentice Hall
– Physical states of substances are indicated by abbreviations:
(g) = gas
(aq) = aqueous (dissolved in H2O)
(s) = solid
(l) = liquid
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– Catalysts
• Speed up a reaction (lowers the activation energy) without being used in the reaction • Formula of catalyst is written above the arrow
– If heat is supplied to reaction:
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11.1
Describing Chemical
Reactions
>
Writing Chemical Equations
A catalyst is a substance that speeds up the
reaction but is not used up in the reaction.
Without Catalyst
With Catalyst
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© Copyright Pearson Prentice Hall
Describing Chemical
Reactions
>
Writing Chemical Equations
Animation 12
Relate chemical symbols and formulas to the
information they communicate.
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© Copyright Pearson Prentice Hall
• Skeleton equations:
– Unbalanced equations (no coefficients)
– 1st step in writing a correct equation – Formulas of reactants and products are written correctly! (just not with the relative amounts using coefficients yet)
– Indicates the state of each substance
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• Writing chemical formulas:
– Remember diatomic elements
– Remember polyatomic ions
– Balance the charges in formula units (ionic compounds) – Roman Numerals indicate the charge on an ion
– Prefixes indicate number of atoms in molecules (covalent compounds)
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• Write a skeleton equation for the following reaction:
– Sulfur burns in oxygen to form sulfur dioxide gas. Slide
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Use the table on pg.
257 for help with the
formula for the
polyatomic ion
“hydrogen carbonate”.
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11.1 Section Quiz.
Propane gas reacts with oxygen to produce water vapor and carbon dioxide. Choose the correct word equation for this reaction. A. propane + carbon dioxide → water + oxygen
B. propane + oxygen + water → carbon dioxide
C. propane + oxygen + water + carbon dioxide
D. propane + oxygen → water + carbon dioxide
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© Copyright Pearson Prentice Hall
11.1 Section Quiz.
Which of the following is a skeleton equation?
A. H2 + CO → CH3OH
B. 2H2 + CO → CH3OH
C. 2H2 + CO2 → CH3OH
D. hydrogen + carbon monoxide → methanol
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© Copyright Pearson Prentice Hall
• Read 11.1 pg. 321‐329
• Q’s 38‐40, pg. 347
• GRSW: due next Fri. (Feb 4th)
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