Chemistry

• Allotropes of carbon are different structural forms of the same element in the same physical state
• Carbon in its solid state can exist in different forms like diamond, graphite, or fullerenes
• Diamond and graphite are both giant covalent structures made of a regular lattice of covalently bonded atoms
• In diamond, each carbon atom is covalently bonded to four other carbon atoms, forming a regular 3D pattern
• Diamond is very strong with a high melting point, but it does not conduct electricity due to the lack of free electrons or ions
• In graphite, each carbon atom is bonded to only three other carbon atoms, forming large flat sheets arranged on top of one another
• The individual layers in graphite are weakly held together, allowing them to slide over one another, making graphite relatively soft
• Graphite still has a high melting point due to the strong covalent bonds within the individual layers
• Each carbon atom in graphite has one spare electron that becomes delocalized, allowing graphite to conduct electricity and heat
• A single layer of graphite is known as graphene, which can be isolated and used to make other structures like spheres and tubes
• Effect on rate of reaction of changes in temperature, concentration, pressure, and surface area

  Increasing temperature, concentration, pressure, and surface area increases the rate of reaction
• Effects on rates of reaction of changes in temperature, concentration, and pressure in terms of frequency and energy of collision between particles

  Increasing temperature increases the rate of reaction. As temperature increases, the speed of the moving particles increases, leading to more frequent and energetic collisions. Increasing concentration of reacting solutions increases the rate of reaction by increasing the frequency of collisions. Increasing pressure of reacting gases increases the rate of reaction by increasing the frequency of collisions
• Effects on rates of reaction of changes in the size of the pieces of a reacting solid in terms of surface area to volume ratio

  A greater surface area to volume ratio means a greater rate of reaction. Increasing surface area to volume ratio provides more surfaces for a reaction to occur, increasing the frequency of collisions and therefore increasing the rate
• Catalysts


  • Substances that speed up chemical reactions without being changed or used up during the reaction (enzymes are biological catalysts)
• Catalysts speed up chemical reactions without being changed or used up during the reaction
• Enzymes are biological catalysts
• Catalysts are substances that speed up chemical reactions without being changed or used up during the reaction
• Strong acids completely dissociate into H+ ions when they dissolve in water, while weak acids only partially dissociate.
• Aqueous solutions with a pH less than 7 are acidic, while those with a pH greater than 7 are basic (alkaline).
• The pH scale is logarithmic, meaning that a change of one unit on the pH scale represents a tenfold increase or decrease in hydrogen ion concentration.
• The pH scale is logarithmic, meaning that each whole number change represents a tenfold increase/decrease in acidity/alkalinity.
• Acidic solutions have a pH less than 7, neutral solutions have a pH equal to 7, and alkaline solutions have a pH greater than 7.
• The pH scale is logarithmic, meaning that a change of one unit on the pH scale represents a tenfold increase/decrease in hydrogen ion concentration.
• Indicators can be used to determine whether an unknown solution is acidic, basic, or neutral by changing color based on their own pKa values.
• Acid-base indicators can be used to determine whether an aqueous solution is acidic or alkaline by changing color based on their pKa value.
• Indicators have different colors at different pH values due to changes in the equilibrium between the indicator molecule and its conjugate base.
• Each whole number change on the pH scale represents a tenfold increase/decrease in acidity/alkalinity.
• Neutral substances have a pH value close to 7.
• Bases react with acids to form salts and water.
• In a buffer system, the addition of small amounts of strong acid or base does not significantly affect the pH because it is resisted by the large amount of conjugate base or acid present.
• A buffer system consists of a weak acid and its conjugate base, which work together to resist changes in pH when small amounts of strong acids or bases are added.
• Weak bases do not fully dissociate in solution.