Chemical Changes (College Board AP® Chemistry): Flashcards
0Still learning
Know0
Define physical change.
Was this flashcard helpful?
Cards in this collection (27)
Define physical change.
A change in the appearance or state of matter in which the internal composition of the substance remains the same.
True or False?
All changes of state are physical changes.
True.
During changes of state, particles change their arrangement and intermolecular forces but retain their chemical identity — no new substances are formed.
Define chemical change.
A change in which the internal composition of a substance is altered — atoms from the original substances rearrange to form new substances that are chemically different from the originals.
What are three observable indicators that a chemical change has occurred?
A change in colour, the formation of a precipitate (an insoluble compound in aqueous solution), or the production of heat or light.
When a mixture of salt and water is separated by simple distillation, this is classified as a .......... change because the components do not lose their internal structure.
When a mixture of salt and water is separated by simple distillation, this is classified as a physical change because the components do not lose their internal structure.
True or False?
In a chemical change, the internal composition of the substance stays the same.
False.
In a chemical change, atoms rearrange to form new substances with a different chemical composition — this is what distinguishes chemical changes from physical ones.
Why is the formation of a precipitate considered evidence of a chemical change rather than a physical change?
A precipitate is an insoluble solid formed from ions in solution — it is a new substance with a different chemical identity from the reactants, indicating that atoms have rearranged during the reaction.
Define spectator ion.
An ion that appears unchanged on both sides of a complete ionic equation — it does not participate in the reaction and is removed when writing the net ionic equation.
What are the four state symbols used in balanced equations, and what does each represent?
(s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous (dissolved in water).
A .......... ionic equation is obtained by removing the spectator ions from the complete ionic equation, leaving only the species directly involved in the reaction.
A net ionic equation is obtained by removing the spectator ions from the complete ionic equation, leaving only the species directly involved in the reaction.
True or False?
A molecular equation shows all soluble compounds separated into their individual ions.
False.
A molecular equation shows the complete chemical formula of each reactant and product. It is the complete ionic equation that breaks soluble compounds into their separate ions.
What is the difference between a complete ionic equation and a net ionic equation?
A complete ionic equation shows all soluble compounds separated into their ions; a net ionic equation removes the spectator ions, leaving only the species that actually react.
True or False?
In a balanced ionic equation, the total charge must be the same on both sides.
True.
Charge is conserved in both complete ionic equations and net ionic equations — the sum of charges on the left must equal the sum on the right.
In a balanced chemical equation, what do the coefficients represent?
The coefficients represent the number of molecules (or moles) of each substance involved in the reaction — they show the ratio in which reactants combine and products form.
Why must a chemical equation be balanced before performing any stoichiometric calculation?
Atoms cannot be created or destroyed — the number of atoms of each element must be the same on both sides. A balanced equation ensures the correct mole ratios are used in calculations.
When balancing a chemical equation, you adjust the .......... (numbers in front of formulas) — never the subscripts (numbers within formulas).
When balancing a chemical equation, you adjust the coefficients (numbers in front of formulas) — never the subscripts (numbers within formulas).
True or False?
When balancing equations, atoms in compounds should be balanced before atoms present as pure elements.
True.
Atoms in the most complex substances (compounds) are balanced first because adjusting their coefficients affects multiple elements at once; pure elements are adjusted last.
What step must be taken if balancing an equation produces a fractional coefficient?
Multiply all coefficients in the equation by the denominator of the fraction to clear it, giving the smallest set of whole-number coefficients.
In the reaction Al + CuO → Al2O3 + Cu, what is the correctly balanced equation?
2Al + 3CuO → Al2O3 + 3Cu
Balancing order: O first (place 3 before CuO), then Cu (place 3 before Cu), then Al (place 2 before Al).
True or False?
Changing the subscripts in a chemical formula is a valid method for balancing a chemical equation.
False.
Changing subscripts alters the chemical identity of the substance itself. Only coefficients — the numbers placed in front of formulas — may be changed when balancing.
During a physical process, which types of interactions change and which remain the same?
Intermolecular forces (e.g. hydrogen bonding, dipole-dipole, London dispersion forces) are broken or reformed, but the intramolecular bonds within each molecule remain unchanged — the chemical identity is preserved.
Bond breaking .......... energy; bond formation .......... energy.
Bond breaking requires energy; bond formation releases energy.
True or False?
When liquid water turns to steam, the polar covalent O–H bonds within water molecules are broken.
False.
Only the intermolecular hydrogen bonds between water molecules are broken during vaporisation. The intramolecular O–H covalent bonds remain intact because the chemical identity of water does not change.
Define ion-dipole interaction.
An electrostatic attraction between an ion and the oppositely charged end of a polar molecule — for example, between Na+ and the oxygen end of water when NaCl dissolves.
When NaCl dissolves in water, ionic bonds in the lattice break and ion-dipole interactions form. Why is this still classified as a physical process?
Dissolution is classified as physical because no new chemical species are formed — Na+ and Cl- ions exist in both the solid lattice and in solution, and the process is reversible by evaporation. The AP CED classifies ionic dissolution as physical despite the ion-dipole interactions involved.
True or False?
During a chemical process, the chemical identity of the products is different from that of the reactants.
True.
Chemical processes involve the breaking and formation of chemical bonds, producing substances with a different internal structure and chemical identity from the starting materials.
When H2 burns in O2 to form H2O, which bonds are broken and which are formed?
H–H bonds and the O=O bond are broken (requiring energy); four O–H bonds are formed in the water products (releasing energy). The rearrangement of covalent bonds makes this a chemical process.
Sign up to unlock flashcards
or