Stoichiometry
The relation between the quantities
of substances that take part in a reaction or
form a compound.
The
proportional
relationship
between two or more substances during a
chemical equation.
Based on one amount of a
substance in a chemical equation, you will
be able to calculate the amount of any other
substance in a reaction.
IMPORTANT CONCEPTS:
1. You must have a balanced equation.
2. The coefficients of the equation
describe the amounts of each substance
in moles.
3. A balanced equation is a recipe for the
reaction. It must be followed.
Steps to Solve Stoichiometry
1. Convert any masses given to moles.
Mass of substance (g) / Molar mass of
substance (g/mol) = number of moles
2. Determine the mole ratio needed.
3. Use the mole ratio to determine the
amount of product known reactant will
produce. (Known Moles x Mole Ratio =
Moles of Product)
4. Convert moles of product to grams.
Number of moles x Total molar mass =
Mass of substance (g).
Limiting Reactant
The limiting reactant is the reactant that is
completely consumed in a chemical
reaction.
Steps for Calculating Limiting
Reactants
1. Balance the equation
2. Label the known substances and
the unknown substance for each
reactant (note: you will have 2
problems)
3. Convert from mass to moles for
each reactant
4. Use a mole ratio for each of the
known substances for each reactant
5. Use the molar mass to convert from
moles to mass for each reactant
6. Look for the lowest number- this is
your limiting reactant.
DEFINITIONS:
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Thermodynamics is the study of
processes in which energy is
transferred as work and heat.
Thermochemistry is the study of how
energy in the form of heat is consumed
and produced by chemical reactions
The system is a set of particles we wish
to study.
Energy is anything having the capacity
to do work or to transfer heat.
The environment is everything else.
Heat (Q) is the transfer of energy into
or out of the system by a temperature
difference.
Work (W) is the transfer of energy into
or out of the system by a force. Force x
Distance.
Internal Energy (U) is the sum of the
kinetic and potential energies of all the
particles in the system.
LAWS OF THERMODYNAMICS
Zeroeth Law
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Temperature; Two systems in
equilibrium with a third system are
in thermal equilibrium with each
other.
First Law
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Conservation Energy; Energy can
change forms, but is neither created
nor destroyed.
Second Law
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Entropy of an isolated system
always increases.
Thermochemistry
Exothermic Reaction
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Endothermic Reaction
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Entropy of a system approaches a
constant
as
temperature
approaches absolute zero.
Is a reaction that absorbs heat from
the surrounding.
Temperature of the surrounding
decreases.
H = positive
Enthalphy
The energy contained in chemical
bonds that can be converted into heat is
known as enthalphy and is given the symbol
H.
It is impossible to measure the
actual heat content or enthalphy of a
particular substance but what can be readily
measured is the enthalphy change for
reaction, H.
Heat of Reaction (Hrxn)
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Amount of heat energy given off or
absorbed in a particular chemical
reaction for given amount of reactants
or products.
The standard heats of formation
equations combine to produce the
desired equation.
Hrxn = Hf (products) - Hf (reactants)
Third Law
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Is a reaction that release heat to the
surrounding.
Temperature of the surrounding
increases.
H = negative
Heat of Formation (Hf)
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The change of enthalphy when one
mole of a compound is formed from
its constituent enemy.
Gives the change enthalphy during
the formation of a compound.
First Law
E = Q – W
The net change in total of a system (E) is
equal to the heat added to the system (Q)
minus work done by the system (W).
Second Law
In all the spontaneous processes, the
entropy of the universe increases.
Third Law
The value of entropy of a completely pure
crystalline substance is zero at absolute zero
temperature.
Hess’s Law
A chemical equation that can be written as
the sum of two or more steps, the
enthalphy change for the overall equation is
the sum of the enthalphy changes for the
individual steps.
LAWS OF THERMODYNAMICS
Zeroeth Law
If two bodies A and B are in thermal
equilibrium with third body C, then body A
and B are also in thermal equilibrium with
each other.