Chemical Reactions. Reactions and Equations Chapter 10, Section 1. Evidence of Chemical Reactions. Chemical Reaction: the process by which the atoms of one or more substances are rearranged to form different substances Break down food to produce energy Produce natural fibers, cotton and wool.
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Reactions and Equations
Chapter 10, Section 1
reactant 1 + reactant 2product 1 + product 2
Reactants written to the left of the arrow
Products are written to the right of the arrow
Arrow is read as “react to produce” or “yields”.
First write the chemical formulas for the reactants to the left of the arrow including their physical states.
C(s) + S(s)
Finally write the chemical formula for the product, liquid carbon disulfide to the right of the arrow, indicating its physical state.
C(s) + S(s) CS2(l)
1. Write the skeleton equation for the reaction.
ex. H2(g) + Cl2(g) HCl(g)
2. Count the atoms of the elements in the reactants.
ex. H2 2 atoms of H
Cl2 2 atoms of Cl
3. Count the atoms of the elements in the products.
ex. HCl 1 atom H + 1 atom Cl
4. Change the coefficients to make the number of atoms of each element equal on both sides of the equation. Never change a subscript!!
ex. H2(g) + Cl2(g) 2HCl(g)
5. Write the coefficient in their lowest possible ratio.
ex. (2:2) (1:1)
6. Check your work.
2NaOH(aq) + CaBr2(aq) Ca(OH)2(s) + 2NaBr(aq)
Classifying Chemical Reactions
Chapter 10, Section 2
Reactions in Aqueous Solutions
Chapter 10, Section 3
2NaOH(aq) + CuCl2(aq) 2NaCl(aq) + Cu(OH)2(s)
In solution, these exist as ions. When their solutions are mixed, a precipitate of copper (II) hydroxide forms.
Ionic equations are written to show the details of the reaction.
2Na+(aq) + 2OH-(aq) + Cu2+(aq) + 2Cl-(aq) 2Na+(aq) + 2Cl-(aq) + Cu(OH)2(s)
HBr(aq) + NaOH(aq) H2O(l) + NaBr(aq)
Complete Ionic Equation:
H+(aq) + Br-(aq) + Na+(aq) + OH-(aq) H2O(l) + Na+(aq) + Br-(aq)
Crossing out the spectator ions leaves us with:
H+(aq) + OH-(aq) H2O(l)
(net ionic equation)
2HI(aq) + Li2S(aq) H2S(g) + 2LiI(aq)
2H+(aq) + 2I-(aq) + 2Li+(aq) + S2-(aq) H2S(g) + 2Li+(aq) + 2I-(aq)