Chemical Reactions All chemical reactions involve changing substances
Chemical Reactions All chemical reactions involve changing substances. • One or more substances (reactants) change into one or more new substances (products) • We separate products from reactants with an arrow. �� • The arrow means “yields” or “reacts to produce” reactants ��products
How are chemical changes explained? Dalton’s atomic theory tells us: • in a chemical reaction, the ways atoms are joined together are changed. • The atoms themselves are not created or destroyed. • The atoms in the products are the same atoms that were in the reactants.
• Because of these facts, we can represent chemical reactions as equations. • In word equations, such as Iron + oxygen �� iron (III) oxide • The reactants are always on the left, the products on the right. • In this case, Fe + O 2 �� Fe 2 O 3
Fe + O 2 ��Fe 2 O 3 • What’s wrong with this equation? • This equation just shows the formulas of the reactants and products – a skeleton equation. • Skeleton equations do not indicate the relative amounts of reactants and products.
Information about the physical state of a substance is also important: • Fe (s) + O 2 (g) > • Other symbols include (l) and (aq). Fe 2 O 3 (s)
Balancing Chemical Equations • Write the correct formula for the reactants and the products. • Write the formulas for the reactants on the left and the formulas for the products on the right, with a �� in between. Add a “+” for more than one product or reactant. • Count the number of atoms of each element and/or polyatomic ion. (Polyatomic ions can be considered a separate unit) • balance the chemical equation using coefficients for each element.
What is a coefficient? • A small whole number that appears in front of a chemical formula in a reaction. • Check each atom or polyatomic ion to make sure the equation is balanced. • Check to see if the coefficients are in the lowest possible ratio.
Why is balancing necessary? • The law of conservation of mass must be maintained. • In a balanced equation, each side has the same number of atoms of each element.
Examples of Balancing Equations Zinc reacts with oxygen to produce zinc oxide. Zn(s) + O 2(g) �� Zn. O(s) skeleton Potassium chlorate is heated, decomposing into potassium chloride and oxygen gas KCl. O 3 (s) ��KCl(s) + O 2 (g)
Types of Chemical Reactions 2 Zn(s) + O 2(g) �� 2 Zn. O(s) A + B �� AB Making a compound from two elements (or two compounds) is called a synthesis reaction 2 KCl. O 3 (s) �� 2 KCl(s) + 3 O 2 (g) AB �� A + B The breaking apart of a compound into elements and/or compounds is called a decomposition reaction
Two Other Types of Reactions Single Replacement K(s) + H 2 O (l) �� KOH(aq) + H 2(g) Double Replacement KI(aq) + Pb(NO 3)2(aq) �� KNO 3(aq) + Pb. I 2 (s)
Zn + HCl �� Zn. Cl 2 + H 2 O Na. Cl. O 3 �� Na. Cl + O 2 P 4 + Cl 2 �� PCl 3 HCl + Mg(OH)2 �� Mg. Cl 2 + Ba. O + SO 3 �� Ba. SO 4 Pb + Ag. NO 3 Ag + Ag. NO 3 + �� Na 2 Cr. O 4 �� Ag 2 Cr. O 4 + Pb(NO 3)2 Na. NO 3 H 2
Al + Fe 3 O 4 �� Al 2 O 3 + NO 2 �� NO + O 2 Na 3 N ��Na + N 2 Pb(NO 3)2 + KI �� KNO 3 Ca. O + CO 2 �� Ca. CO 3 Fe + Pb. I 2 Mg. CO 3 ��Mg. O + HNO 3 + �� Mg(NO 3)2 + H 2 O Mg(OH)2 CO 2
Ca + H 2 O �� Ca(OH)2 Fe + O 2 �� Fe 2 O 3 Cl 2 + KI �� KCl + Ba(NO 3)2 + Ag 2 O + I 2 Na 2 SO 4 ��Ba. SO 4 + �� Ag + O 2 H 2 Na. NO 3
More Equations Fe + O 2 �� P 4 O 10 + C 3 H 8 + Hg. O Sr. Br 2 + Fe 2 O 3 H 2 O �� H 3 PO 4 O 2 �� Hg + �� CO 2 + H 2 O O 2 (NH 4)2 CO 3 �� Sr. CO 3 + Al + O 2 �� Al 2 O 3 Al + Ag. NO 3 �� Al(NO 3)3 + NH 4 Br Ag
Al + HCl F 2 + Au 2 O 3 �� Al. Cl 3 + HCl ��HF + �� Au + NH 4 NO 3 �� N 2 O + H 2 SO 4 + Xe + Na. OH H 2 Cl 2 O 2 H 2 O �� Na 2 SO 4 + F 2 �� Xe. F 6 Ca(Cl. O)2 ��Ca. Cl 2 + H 2 O
Fe + H 2 O ��Fe 2 O 3 + Fe 2(SO 4)3 + KOH �� H 2 K 2 SO 4 N 2 + O 2 �� N 2 O Mg + Cu. Cl 2 �� Mg. Cl 2 + KCl. O 3 �� KCl. O 4 + K 2 O + Fe(OH )3 Cu KCl H 2 O �� KOH I 4 O 9 �� I 2 O 6 + • + I 2 + O 2 This last one has many possible solutions!!!
“Mother of All Equations” Joined: 18 Nov 2006 Posts: 1 Posted: Sat Nov 18, 2006 8: 47 am Post subject: "mother of all equations" Hello, I need a some help with homework. My teacher considers this the "mother of all equations" and she gave it to us to solve. . . I need to balance the following equation, charges included, this reaction takes place in an aqueous solution. [Cr(N 2 H 4 CO)6]4[Cr(CN)6]3 + KMn. O 4 + H 2 SO 4 =(this is an arrow)= K 2 Cr 2 O 7 + Mn. SO 4 + CO 2 + KNO 3 + K 2 SO 4 + H 2 O
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