5 Chemical Reactions and Stoichiometry Free Online FlashCards

What does the subscript in $\mathrm{H_2O}$ specify?

Subscripts show how many atoms of each element are in one molecule or formula unit; in $\mathrm{H_2O}$, each molecule has two hydrogen atoms and one oxygen atom.

What does a coefficient count in $2\mathrm{H_2O}$?

A coefficient counts how many entities or moles of a substance are involved. For example, $2\mathrm{H_2O}$ represents two water molecules or two moles of water, depending on context.

How many specified entities are in one mole?

One mole contains exactly $6.02214076 \times 10^{23}$ specified entities, such as atoms, molecules, ions, or formula units.

What is the molar mass of water?

Molar mass is the mass of one mole of a substance, usually expressed in grams per mole. For water, $M = 2(1.008) + 16.00 = 18.016\ \mathrm{g/mol}$.

How do you convert a sample’s mass to moles?

Use $n = \frac{m}{M}$: divide the sample mass $m$ in grams by the molar mass $M$ in grams per mole.

What must a balanced chemical equation conserve?

A balanced equation has the same number of atoms of each element on both sides. For ionic equations, total charge must also be conserved.

What may you change to balance a chemical equation?

Change coefficients only. Changing a subscript changes a substance’s identity rather than balancing the original equation.

How do synthesis and decomposition differ?

Synthesis combines simpler substances into a compound, following $A + B \rightarrow AB$. Decomposition splits a compound into simpler substances, following $AB \rightarrow A + B$.

What is the general pattern for single replacement?

In single replacement, an element replaces another element in a compound: $A + BC \rightarrow AC + B$.

What happens in a double-replacement reaction?

In double replacement, parts of two compounds exchange partners: $AB + CD \rightarrow AD + CB$. In aqueous solutions, the reaction may form a precipitate, water, or a gas.

What products often form when a hydrocarbon undergoes combustion?

Combustion occurs when a fuel reacts with $\mathrm{O_2}$. A hydrocarbon often produces $\mathrm{CO_2}$ and $\mathrm{H_2O}$.

What defines a redox reaction?

A redox reaction involves electron transfer, identified by changes in oxidation states.