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AgCl in the reaction vessel. within the reaction. For example,
Reducing the temperature shifts splitting apart the water molecule
the equilibrium position to the (H 2O) into hydrogen and oxygen
right, producing more heat and gases requires adding energy into
more white AgCl. the system (usually in the form of
electricity).
Bond Energy
H 2O + energy H 2 + O 2
By knowing the value of the bond
Electronegativity is how
energy, we can predict if a
attracted an electron is to an atom.
chemical reaction will be
The higher the electronegativity of
exothermic or endothermic. If the
an atom, the greater its attraction
bonds in the products are stronger
for the bonding electrons. Elements
than the bonds in the reactants,
with high ionization energy have
then the products are more stable
high electronegatives because of
and the reaction will give off heat
the strong pull by the nucleus on
(exothermic).
the electrons.
Exothermic Reactions Many
Ionization energy (measured in
chemical reactions release energy
electronvolts, eV) is the amount of
as heat, light, or sound (or all
energy needed to completely
three). Some release heat
remove an electron from gaseous
gradually (for example, a
atom or ion. If the electron is
disposable hand-warmer), while
tightly bound, the ionization energy
others are more explosive (like
levels are higher and it’s harder to
burning magnesium). The energy
remove.
comes from breaking the bonds
within the chemical reaction. The The first ionization energy is the
combination of sodium and chlorine amount of energy needed to
to form table salt and energy: remove one electron from the
atom, and the second ionization
Na + ½ Cl 2 = NaCl + energy
energy is the energy to remove a
Endothermic Reactions Other second electron (and is always a
chemical reactions need to absorb higher value). It’s harder and
energy in order to react. Often harder to remove subsequent
you’ll notice a temperature drop electrons because the electrons are
when the reaction takes place (a closer to the nucleus, which also is
disposable ice pack, for example). more positively charged.
The energy goes to forming new
chemical bonds between molecules
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