7 3 exothermic and endothermic reactions
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7.3 Exothermic and Endothermic Reactions. Review Stuff from 7.1. Chemical reactions involve the breaking of chemical bonds in the reactants and the formation of chemical bonds in the products . Reactants are on the left side Products are on the right side. Law? What law?.

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Review stuff from 7 1
Review Stuff from 7.1

  • Chemical reactions involve the breaking of chemical bonds in the reactants and the formation of chemical bonds in the products.

  • Reactants are on the left side

  • Products are on the right side.


Law what law
Law? What law?

  • During a chemical reaction, mass is neither created or destroyed.

This is defined as……….?

Law of Conservation of Mass


Did you know
Did You Know?

  • Physical changes can release or absorb energy.

    VOCABULARY FOR 7.3

  • Break down the prefix or root words

    • Endo = “in”

    • Exo = “out”

    • Thermic = “heat”


Exo out
Exo = “out”

  • During an exothermic change, such as freezing, energy is released to the surroundings.

  • The energy released as the products form is more than the energy required to break the bonds in the reactants.


Combustion
Combustion

  • An example of an extremely exothermic reaction.

  • Because heat is released, the energy term appears on the right sideof the equation.

  • When 1 mole of propane reacts with 5 moles of oxygen, 2220 kJ (kilojoules) of heat is released.

  • You can use this value to replace “heat” in the combustion equation written earlier.


How to read an exothermic reaction
How to read an exothermic reaction

  • Cu(s) + Cl2(g) → CuCl2(g) + 220.1 kJ

energy is released


Where is the chemical energy is greater
Where is the chemical energy is greater?

  • Cu(s) + Cl2(g) → CuCl2(g) + 220.1 kJ

REACTANTS


Endo in
Endo = “in”

  • During an endothermic change, such as melting, energy is absorbed from the surroundings. Energy also flows into and out of chemical changes.


Decomposition
Decomposition.

  • When mercury(II) oxide is heated to a temperature of about 450°C, it breaks down into mercury and oxygen.

  • The decomposition of mercury(II) oxide is an endothermic reaction that can be described by the following equation.

  • Because heat is absorbed, the energy term appears on the left sideof the equation.

  • For every 2 moles of HgO that decomposes, 181.7 kJ of heat must be absorbed.


How to read an endothermic reaction
How to read an endothermic reaction

  • H2O(g) + C(s) + 132 kJ → CO2(g) + 2H2(g)

energy is absorbed


Where is the chemical energy is greater1
Where is the chemical energy is greater?

  • H2O(g) + C(s) + 132 kJ → CO2(g) + 2H2(g)

PRODUCTS



Identify the reactions below
Identify the reactions below.

  • CH4(s) + 2O2(g) → CO2(g) + 2H2O(l) ΔH° = -890 kJ

  • 2HCl(g) → H2(g) + Cl2(g) ΔH° = 185 kJ

  • 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(l) ΔH° = -1169 kJ

Endothermic

Exothermic

Endothermic


Practice problems
Practice Problems

  • When potassium nitrate dissolves in water, the beaker containing the solution gets cooler.

  • Is dissolving this salt an exothermic or an endothermic process?

Endothermic

The reaction requires heat, which it absorbs from the surroundings (the water). This causes the water temperature to decrease.


Practice problems1
Practice Problems

Endothermic

This reaction cn be identified as…….

Exothermic





The endo

The ENDo

Ha ha – get it?


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