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