Chemistry Balancing Equations and Moles

Note: Some questions are designed for multiple choice answers while some are designed for written answers.

Chemical reactons do what?

Produce new substances

What does the symbol Δ above the arrow in a chemical equation mean?

Heat is supplied to the reaction

Which of the following combinations of symbol and explanation of symbol is correct when used in a chemical equation?

(aq), dissolved in water

In the chemical equation H₂O₂(aq)  ⟶ H₂O(l) + O₂(g), the O₂ is a ____.

product

A catalyst is

a substance that speeds up the reaction but is not itself used up in the reaction

What are the coefficients that will balance the skeleton equation below?
AlCl₃ + NaOH ⟶ Al(OH)₃ + NaCl

1, 3, 1, 3

What are the coefficients that will balance the skeleton equation below?
N₂ + H₂ ⟶ NH₃

1, 3, 2

When the equation Fe + Cl₂ ⟶ FeCl₃ is balanced, what is the coefficient for Cl₂?

3

Which of the following statements is true about what happens in all chemical reactions?

Bonds between atoms are broken and new bonds are formed.

Chemical equations must be balanced to satisfy

the law of conservation of mass.

When the equation KClO₃(s) ⟶ KCl(s) + O₂(g) is balanced, the coefficient of KClO₃ is

2

In every balanced chemical equation, each side of the equation has the same number of ____.

atoms of each element

What are the missing coefficients for the skeleton equation below?
Cr(s) + Fe(NO₃)₂(aq) ⟶ Fe(s) + Cr(NO₃)₃(aq)

2, 3, 3, 2

What are the missing coefficients for the skeleton equation below?
Al₂(SO₄)₃(aq) + KOH(aq) ⟶ Al(OH)₃(aq) + K₂SO₄(aq)

1, 6, 2, 3

In order to predict whether or not a single-replacement reaction takes place, you need to consult a chart that shows the

activity series of metals

In order for the reaction 2Al + 6HCl ⟶ 2AlCl₃ + 3H₂ to occur, which of the following must be true?

Al must be above H on the activity series.

In a combustion reaction, one of the reactants is

oxygen

The products of a combustion reaction include

water, carbon dioxide, and carbon monoxide.

The type of reaction that takes place when one element reacts with a compound to form a new compound and a different element is a ___

single replacement reaction

In a double-replacement reaction, the

reactants are two ionic compounds

Which of the following statements is true about the decomposition of a simple binary compound?

The reactant is a single substance.

Which of the following statements is true about single-replacement reactions?

Two reactants produce two products.

In the activity series of metals, which metal(s) will displace hydrogen from an acid?

only metals above hydrogen

In a double-replacement reaction, one of the products

may precipitate from solution.

In a double-replacement reaction,

the reactants are generally two ionic compounds in aqueous solution.

The complete combustion of which of the following substances produces carbon dioxide and water?

C₈H₁₈

Which of the following is a correctly balanced equation for the incomplete combustion of heptene, C₇H₁₄?

C₇H₁₄ + 7O₂ ⟶ 7CO + 7H₂O

The equation 2Fe + 3Cl₂ ⟶ 2FeCl₃ is an example of which type of reaction?

combination

The equation Mg(s) + 2HCl(aq) ⟶ MgCl₂(aq) + H₂(g) is an example of which type of reaction?

single-replacement reaction

The equation H₃PO₄ + 3KOH ⟶ K₃PO₃ + 3H₂O is an example of which type of reaction?

double-replacement reaction

A double-replacement reaction takes place when aqueous cobalt(III) chloride reacts with aqueous lithium hydroxide. One of the products of this reaction is

Co(OH)₃

Use the activity series of metals to complete a balanced chemical equation for the following single replacement reaction.
Ag(s) + KNO₃(aq) ⟶

No reaction takes place because silver is less reactive than potassium.

What is the driving force in the following reaction?
Ni(NO₃)₂(aq) + K₂S(aq)  ⟶

A precipitate is formed.

If a combination reaction takes place between rubidium and bromine, the chemical formula for the product is ____.

RbBr

What are the correct formulas and coefficients for the products of the following double-replacement reaction?
RbOH + H₃PO₄ ⟶

Rb₃PO₄ + 3H₂O

What is a skeleton equation?

The unbalanced equation before being balanced

Define a combination/synthesis reaction

Two or more substances react to form a single new substance

Describe a decomposition reaction

A single compound breaks down into two or more products

Describe a single replacement reaction

One more reactive element replaces a second less reactive element in a compound (based on activity series for metals. For nonmetals, reactivity increases from left to right and down to up)

Describe a double replacement reaction

Reactant cations exchange places to form new compounds

Predict the products and write the balanced equation for the following single-replacement reaction

Fe(s) + Pb(NO3)2(aq) —> ?

Fe(s) + Pb(NO3)2(aq) —> Fe(NO3)2(aq) + Pb(s)

Predict the products and write the balanced equation for the following single-replacement reaction

F2(aq) + NaCl(aq) —> ?

F2(aq) + 2NaCl(aq) —> Cl2(aq) + 2 NaF(aq)

Predict the products and write the balanced equation for the following single-replacement reaction

Ca(s) + H2O(l) —> ?

Ca(s) + 2H2O(l) —> Ca(OH)2(aq) + H2(g)

Predict the products and write the balanced equation for the following double-replacement reaction

HCl(aq) + AgNO3(aq) —> ?

HCl(aq) + AgNO3(aq) —> AgCl(s) + HNO3(aq)

How do you convert moles to mass (grams)?

Multiply number of moles x molar mass of the atom/compound

What is the molar mass of an atom/compound?

The same as its atomic mass on the periodic table

How do you convert mass (grams) to moles?

Divide the mass by the molar mass of the atom/compound

How do you convert moles to particles?

Multiply number of moles x Avogadro’s number

What is Avogadro’s number?

6.02 × 10^23

How do you convert particles to moles?

Divide number of particles by Avogadro’s number

How do you convert moles to volume (L)?

Multiple number of moles x 22.4 L/mol

What is the molar volume at STP of any gas?

22.4 L/mol

How do you convert volume (L) to moles?

Divide the volume by 22.4 L/mol

What are the seven elements that form diatomic molecules?

Bromine, Iodine, Nitrogen, Chlorine, Hydrogen, Oxygen, Fluorine (BrINClHOF)

How do you write a number in scientific notation?

Shift the decimal so that only one non zero digit is at the front of the number. However many places the decimal was moved is the exponent. If you moved left, the exponent is postive, if right, negative.

How do you calculate the density of a gas at STP from its molar mass?

Divide the molar mass by 22.4 L/mol

How do you calculate percent composition of elements in a compound?

Divide the mass of 1 mol of the element by the molar mass of the compound, then multiply your answer by 100%

How do you find the empirical formula of a compound?

Assume 100-g sample (ex. 65% C = 65 g C), find the moles of each element, divide the results by the smallest number, and round those results to whole numbers.

How do you find the molecular formula of a compound?

Calculate the EFM of the compound, then divide the molar mass of the compound by the EFM. Multiply that result by empirical formula of the compound.

How many hydrogen atoms are in 5 molecules of isopropyl alcohol, C₃H₇O?

35

Which of the following elements exists as a diatomic molecule?

nitrogen

How many moles of tungsten atoms are in 4.8 x 10²⁵ atoms of tungsten?

8.0 x 10¹ moles

How many atoms are in 0.075 mol of titanium?

4.5 × 10^22

How many molecules are in 2.10 mol CO₂?

1.26 x 10²⁴ molecules

The atomic masses of any two elements contain the same number of ____.

atoms

An average bushel of apples has a mass of 10 kg and contains 5 dozen apples.

What would be the average mass of 6 apples?

1.0 kg

What is the molar mass of AuCl₃?

303.6 g

What is the mass in grams of 5.90 mol C₈H₁₈?

673 g

The molar mass of a certain gas is 49 g. What is the density of the gas in g/L at STP?

2.2 g/L

Which of the following gases at STP would have the greatest volume?

5.00 mole of H2

If the density of a noble gas is 1.783 g/L at STP, that gas is ____.

Ar

What is the percent composition of chromium in BaCrO4?

20.5%

What is the percent by mass of carbon in acetone, C₃H₆O?

62.1%

What is the empirical formula of a compound that is 40% sulfur and 60% oxygen by weight?

SO3

The ratio of carbon atoms to hydrogen atoms to oxygen atoms in a molecule of dicyclohexyl maleate is 4 to 6 to 1. What is its molecular formula if its molar mass is 280 g?

C16H24O4

How many representative particles are in 1.45 g of a molecular compound with a molar mass of 237 g?

3.68 × 10^21 particles

The lowest whole-number ratio of the elements in a compound is called the ____.

empirical formula

How many moles of silver atoms are in 1.8 x 10²⁰ atoms of silver?

3.0 x 10^-4