Ch 8 Section 1 Flashcards
a chemical reaction is the process b which one or more substances are
changed into one or more different substances.
in any chemical reaction, the original substances are known as the —– and the resulting substances are known as the
reactants, products
according to the law of conservation of mass, the total mass of reactants must equal the
total mass of products for any given chemical reaction
chemical reactions are described by
chemical equations
a chemical equation represents, with symbols and formulas, the identities and relative molecular or molar amounts of the
reactants and products in a chemical reaction
absolute proof of a substances’ change in identity can be provided only by
chemical analysis of the products
certain easily observed changes usually indicate that a
chemical reaction has occurred
(Observed changes) evolution of energy as
heat and light
(a change in matter that observed changes- evolution of energy as heat and light) a change in matter that releases energy as both
heat and light is strong evidence that a chemical reaction has taken place
(observed changes- evolution of energy as heat and light) heat or light by itself is not necessarily a sign of chemical change because
many physical changes also involve either heat or light
(observed changes- production of a gas) the evolution of gas bubbles when two substancs are mixed is often
evidence of a chemical reaction
(observed changes- formation of a precipitate) many chemical reactions take place between
substances that are dissolved in liquids
(observed changes- formation of a precipitate) if a solid appears after two solutions are mixed, a
reaction has likely occurred
(observed changes- formation of a precipitate) a solid that is produced as a result of a chemical reaction in solution and that
separates from the solution is known as a precipitate
(observed changes- color change) a change in color is often an
indication of a chemical reaction
a properly written chemical equation can summarize any
chemical change
(requirements for writing correct chemical equations) the equation must represent known
facts
(requirements for writing correct chemical equations) all reactants and products must be identified, either through chemical analysis in the lab or from
sources that give the results of experiments
(requirements for writing correct chemical equations) te equation must contain the correct
formulas for the reactants and products
(requirements for writing correct chemical equations) knowledge of the common oxidation stats of the elements and of methods of writing formulas will enable you to supply
formulas for reactants and products if they are not available
(requirements for writing correct chemical equations) diatomic molecules represented in an equation by molecular formula, but other elements are represented simply by their atomic symbols, without subscripts, because the elements do not form
definite molecular structures (exceptions–> S8 and P4)
(requirements for writing correct chemical equations) he law of conservation of mass must be
satisfied
(requirements for writing correct chemical equations) the same number of atoms of each element must appear of
each side of a correct chemical equation
(requirements for writing correct chemical equations) to balance numbers of atos add
coefficients where necessary
(requirements for writing correct chemical equations) a coefficient is a small whole number that appears in front of a
formula in a chemical equation
(requirements for writing correct chemical equations) placing a coefficient in front of a formula specifies the relative number of
moles of the substance (if no coefficient, assumed to be 1)
the first step in writing a chemical equation is to identify the facts to be
represented
a word equation is an equation in which the reactants and products in a chemical reaction are
represented by words
a word equation (qualitative) does not give the whole story because it does not give the quantities of the
reactants used or products formed
the next step in writing a correct chemical equation is to replace the names of the reactants and products with
appropriate symbols and formulas
a formula equation represents the reactants and products of a chemical reaction by their
symbols and formulas
the g in parentheses after each formula indicates that the corresponding substance is in the
gaseous state
a formula equation is a
qualitative statement
a formula equation represents the facts and shows the
correct symbols and formulas for the reactants and products
to complete the process of writing a correct equation, the law of conservation must be
taken into account
the relative amounts of reactants and products represented in the equation must be adjusted so that the number sand types of atoms are the
same on both sides of the equation
process is called balancing an equation and is carried out by
inserting coefficients
sometimes a gaseous product is indicated by an
arrow pointing upward
a downward arrow is often used to show the formulation of a
precipitate during a reaction in solution
the conditions under which a reaction takes place are often indicated by placing
information above or below the reaction arrow
–> “Yields” indicates
result of reaction
—->
reversible reaction
(s) a reactant or product in the
solid state; also indicates precipitates
↓ alternative to (s), but used only to indicate
a precipitate
(l) a reactant or
product in the liquid state
(aq) a reactant or product in an
aqueous solution (dissolved in water)
↑ alternative to (g), but used only to indicate a
gaseous product
∆ heat reactants are
→ →
heated
2 atm
→ pressure at which reaction is
carried out
pressure
→ pressure at which reaction is carried out exceeds normal
atmospheric pressure
0° C
→ temperature at which reaction is
carried out
MnO2
→ formula of catalyst used to alter the
rate of the reaction
for some reactions it is important to specify the pressure at whichthe reaction occurs or to specify that the pressure must be
above normal
many reactions are speeded up and can take place at lower temperatures in the presence of a
catalyst
a catalyst is a substance that changes the rate of a chemical reaction but can be
recovered unchanged
in many reactions, as soon s the products begin to form, they immediately begin to react with each other and
re-form the reactants
the reverse reaction may occur to a greater or lesser degree than the original reaction, depending on the
specific reaction and the conditions
a reversible reaction is a chemical reaction which the products
re-form the original reactants
he chemical equation as a whole is similar to an algebraic equation in that it
expresses an equality
the coefficients of a chemical reaction indicate relative, not absolute, amounts of
reactants and products
a chemical equation usually shows the smallest numbers of atoms, molecules, or ions, that will satisfy the
law of conservation of mass in a given chemical reaction
to obtain larger relative amounts we simply multiply each
coefficient by the same number
the relative masses of the reactants and products of a chemical reaction can be determined from the
reaction’s coefficients
the reverse reaction for a chemical equation has the same relative amounts of
substances as the forward reaction
because a chemical equation is like an algebraic equation, the equality can be read in
either direction
there is important information that is not provided by a
chemical equation
a chemical equation gives no indication of whether a reaction will
actually occur
a chemical equation can be written for a reaction that may
not even take place
experimentation forms the basis for confirming that a particular
chemical reaction will occur
chemical equations give no info about the speed at which reactions occur or about
how the bonding between atoms or ions changes during the reaction
(balancing chemical equations) identify the names of the reactants and the
products and write a word equation
(balancing chemical equations) write a formula equation by substituting correct formulas for the
names of the reactants and the products
(balancing chemical equations) balance the formula equation according to the
law of conservation of mass
(balancing chemical equations) count atoms to be sure that the
equation is balanced
occasionnaly when counting the atoms, the coefficients do not represent the smallest possible
whole-number ratio of reactants and products
when this happens, the coefficients should be divided by their greatest common fact in order to obtain the
smallest possible whole number coefficients
