Describing chemical reactions 8.1 chem
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"Yields" indicates result of reaction
Physical indicators of chemical reactions
1. Evolution of energy as heat and light 2. Color change 3. Production of a gas 4. Formation of a precipitate
When the equation Fe3O4+ Al —> Al2O3 + Fe is correctly balanced, what is the coefficient of Fe
9
(aq)
A reactant or product in an aqueous solution (dissolved in water)
(g)
A reactant or product in the gaseous state
(l)
A reactant or product in the liquid state
(S)
A reactant or product in the solid state; also used to indicate a precipitate
Upward arrow
Alternative to (g), but used only to indicate a gaseous product
Downward arrow
Alternative to (s), but used only to indicate a precipitate
___ are neither created nor destroyed in ordinary chemical reactions
Atoms
The word equation solid carbon + oxygen gas —> carbon dioxide gas + energy, represents a chemical reaction because
CO2 has chemical properties that differ from those of C and O
Chemical equations must satisfy the law of ___
Conservation of mass
A representation of the reactants and products of a chemical reaction by their symbols or formulas
Formula equation
MnO2 with arrow
Formula of catalyst, in this case manganese dioxide, used to alter the rate of the reaction
In the word equation, sodium oxide + water —> sodium hydroxide, the formula for sodium hydroxide is represented by
NaOH
Chemical reactions have ___ ___
Physical indicators
pressure with arrow
Pressure at which reaction is carried out exceeds normal atmospheric pressure
2 atm
Pressure at which reaction is carried out, in this case 2 atm
Delta
Reactants are heated
0°C with arrow
Temperature at which reaction is carried out, in this case 0°C
The first step in writing a chemical equation
The first step in writing a chemical equation is to identify the facts to be represented
What does g in parentheses mean
The g in parentheses after each formula indicates that the corresponding substance is in the gaseous state
How is the reversibility of a reaction shown
The reversibility of a reaction is indicated by writing two arrows pointing in opposite directions
How do you balance an equation?
To balance the equation, begin by counting atoms of elements that are combined with atoms of other elements and that appear only once on each side of the equation
T or F A change in matter that releases energy as both heat and light is strong evidence that a chemical reaction has taken place
True
T or F A chemical equation can be written for a reaction that may not even take place
True
T or F A properly written chemical equation can summarize any chemical change
True
T or F All reactants and products must be identified, either through chemical analysis in the laboratory or from sources that give the results of experiments
True
T or F Chemical equations can be balanced with step-by-step inspection
True
T or F Chemical equations show relative amounts, masses, and progression of chemical reactions
True
T or F For instance, an equation gives no indication of whether a reaction will actually occur.
True
T or F Like a word equation, a formula equation is a qualitative statement. It gives no information about the amounts of reactants or products
True
T or F The coefficients of a chemical reaction indicate relative, not absolute, amounts of reactants and product
True
T or F The relative amounts of reactants and products represented in the equation must be adjusted so that the numbers and types of atoms are the same on both sides of the equation
True
T or F The relative masses of the reactants and products of a chemical reaction can be determined from the reaction's coefficients
True
T or F The reverse reaction for a chemical equation has the same relative amounts of substances as the forward reaction
True
T or F The reverse reaction may occur to a greater or lesser degree than the original reaction, depending on the specific reaction and the conditions
True
T or F The specific temperature at which a reaction occurs may also be written over the arrow
True
T or F To complete the process of writing a correct equation, the law of conservation of mass must be taken into account.
True
T or F To know for certain that a chemical reaction has taken place requires evidence that one or more substances have undergone a change in identity
True
Arrows going in opp directions
Used in place of a single arrow to indicate a reversible reaction
For example, sometimes a gaseous product is indicated by an __, instead of (g)
arrow pointing upward,↑
This process is called ____ and is carried out by inserting coefficients.
balancing an equation
Many reactions are speeded up and can take place at lower temperatures in the presence of a ___.
catalyst
To show that a ___ is present, the formula for the catalyst or the word catalyst is written over the reaction arrow
catalyst
is a substance that changes the rate of a chemical reaction but can be recovered unchanged
catalyst
A representation of a chemical reaction that uses symbols to show the relationship between the reactants and the products
chemical equation
Chemical reactions are described by ___ ___
chemical equations
A ___ ___ is the process by which one or more substances are changed into one or more different substances.
chemical reaction
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
A ___ is a small whole number that appears in front of a formula in a chemical equation.
coefficient
a small whole number that appears in front of a formula in a chemical equation
coefficient
One must use only ___ to change the relative number of atoms in a chemical equation because coefficients change the numbers of atoms without changing the identities of the reactants or products.
coefficients
To balance numbers of atoms, add ___ where necessary.
coefficients
According to the law of ___, the total mass of reactants must equal the total mass of products for any given chemical ___.
conservation of mass reaction
The word heat, which is symbolized by a Greek capital ___, indicates that the reactants must be heated
delta (Δ)
A ___, is often used to show the formation of a precipitate during a reaction in solution.
downward arrow, ↓
Some elements are represented simply by their atomic symbols when they are in their ___ state.
elemental
The arrow in a balanced chemical equation is like an ___ ___
equal sign
A ___ represents the reactants and products of a chemical reaction by their symbols or formulas
formula equation
However, this would be a mistake because changing the subscripts of a chemical formula changes the ___ of the compound
identity
Placing a coefficient in front of a formula specifies the relative number of ___ of the substance
moles
When a solid produced by a chemical reaction separates from the solution it is called
precipitate
A word equation has only___ (descriptive) meaning. It does not give the whole story because it does not give the ____ of reactants used or products formed.
qualitative quantities
Chemical equations are very useful in doing ___ chemical work
quantitative
The arrow, →, is read as ___ or ___ (also produce or form
react to yield or yield
In many reactions, as soon as the products begin to form, they immediately begin to react with each other and re-form the ___
reactants
In any chemical reaction, the original substances are known as the ___ and the resulting substances are known as the ___
reactants and products
A ___ is a chemical reaction in which the products re-form the original reactants
reversible reaction
a chemical reaction in which the products re-form the original reactants
reversible reaction
A chemical equation usually shows the ___ numbers of atoms, molecules, or ions that will satisfy the law of conservation of mass in a given chemical reaction
smallest
The symbols are not given any subscripts because the elements do not form definite molecular structures. Two exceptions are ___, which is usually written S8, and ___, which is usually written P4.
sulfur phosphorus
In a chemical reaction
the mass of the reactants equals the mass of the products
It is often helpful to write a ___, an equation in which the reactants and products in a chemical reaction are represented by words
word equation
an equation in which the reactants and products in a chemical reaction are represented by words
word equation
Requirements to read and write chemical equations
1. The equation must represent known facts 2. The equation must contain the correct formulas for the reactants and products 3. The law of conservation of mass must be satisfied