Ch 5.1 The Nature of Chemical Reactions

Ch 6.1
Chemical Reactions
Objectives For this Chapter
• Understand parts to a chemical equation
(reactants, products, yeild sign, double
• Conservation of matter is expressed
through balancing chemical equations
• Describe difference between
endothermic and exothermic reactions
Review from Ch 2
Chemical Change: Atoms in the
reactants are rearranged to form
one or more different substances
• Old bonds are broken; new bonds form
Fe and O2 form rust (Fe2O3)
Ag and S form tarnish (Ag2S)
Basic Chemical Equation
______ + _______
Chemical Reaction
A process in which at least one new
substance is produced as a result of
a chemical change
Signs of a chemical reaction
• In nature: grow, ripen, decay, burn
• In the lab: bubbles, change in color,
precipitate forms, light and heat
1. The hydrogen peroxide
oxidizes the phenyl oxalate
ester, resulting in a chemical
called phenol and an unstable
peroxyacid ester.
2. The unstable peroxyacid
ester decomposes, resulting in
additional phenol and a cyclic
peroxy compound.
3. The cyclic peroxy
compound decomposes to
carbon dioxide.
4. This decomposition
releases energy to the dye.
5. The electrons in the dye
atoms jump to a higher level,
then fall back down, releasing
energy in the form of light.
Energy and Reactions
• Energy needed to break bonds and form
new compounds
• Energy is released when new compounds
are formed
• Energy is conserved. Total energy before
reaction = total energy of products
Exothermic reaction - reaction that gives off
heat energy – feels hot
Endothermic reaction - reaction that
absorbs heat energy – feels cold