Chemical Reactions, Acids and Bases flashcards

Only the coefficients in front of formulas. Changing a subscript changes the substance (H2O to H2O2 turns water into hydrogen peroxide). Balanced: $2{\text{H}}_2+{\text{O}}_2\to 2{\text{H}}_2\text{O}$.

Total mass of products equals total mass of reactants because atoms are only rearranged. In an open container a gas product can escape, so the reading drops; in a sealed one it stays the same.

$\text{ratio}=10^{\Delta \text{pH}}$. Each pH unit is a tenfold change, so pH 3 has $10^2=100$ times the hydrogen-ion level of pH 5. The lower pH is more acidic.

Acids: pH below 7, turn blue litmus red, donate protons (H+). Bases: pH above 7, turn red litmus blue, accept protons or add OH-. pH 7 is neutral.

A salt plus water: ${\text{H}}^{+}+{\text{OH}}^{-}\to {\text{H}}_2\text{O}$. The salt combines the base's metal ion with the acid's negative ion, e.g. HNO3 + KOH gives KNO3 + H2O.

Exothermic reactions release energy, so surroundings warm (burning, hand warmers). Endothermic reactions absorb energy, so surroundings cool (instant cold packs, photosynthesis). Neither label says how fast a reaction goes.

A substance that speeds a reaction by lowering activation energy and is not used up (enzymes are biological catalysts). It does not change the overall energy released or the final amount of product.

Strength is how completely the acid ionizes in water (HCl is strong, acetic acid is weak). Concentration is how much acid is dissolved per volume. A dilute strong acid can have a higher pH than a concentrated weak one.