How Chemicals React

How Chemicals React, Acids and Bases

By Abby Fancsali

Chemical Equations

• ​During a chemical reaction, atoms rearrange to form new compounds

• We show this in written form as a chemical equation

  • Reactants: substances that you start with

  • Products: ​Substances that you end with

  • Components are shown with their chemical formulas

    • Numbers in front of the formulas tell you the ratio needed for a reaction to take place

  • States of matter are also shown

    • (s)-Solid, (g)-Gas, (l)-Liquid

Law of Mass Conservation

• One of the most important principles of Chemistry

• Matter is neither created nor destroyed during a chemical reaction

  • You can not gain or add atom during a reaction, the amount you start with is the amount you end with

  • Chemical Equations need to be balanced in order to work​

    • You add coefficients in front of the symbols to multiply how many you have

      • Coefficients must be whole numbers

Balancing Equations

• Lets write at the equation of combining hydrogen and oxygen to make water

  • Start with the names: Hydrogen + Oxygen →​ Water

  • Now change the names to symbols: H₂ + O₂ →​ H₂O

    • Lets count how many of each element we have on both sides of the equation

      • Reactants: 2 hydrogen, 2oxygen

      • Products: 2 hydrogen, 1 oxygen

    • This equation is not balanced, so we need to add coefficients to each of these values to balance the equation

Balancing Equations- adding coefficients

• In the unbalanced form, we can read this equation as 1 H₂ + 1 O₂ →​ 1 H₂O

  • Our Oxygen is unbalanced, so what w​hat whole number can we put in front of the H₂O instead of 1 to balance it out?

Balancing Equations- adding coefficients

• In the unbalanced form, we can read this equation as 1 H₂ + 1 O₂ →​ 1 H₂O

  • Our Oxygen is unbalanced, so what w​hat whole number can we put in front of the H₂O instead of 1 to balance it out?

• When we add a two, the new equation reads: 1 H₂ + 1 O₂ →​ 2 H₂O

  • ​Check for Balance: Reactants have 2 Hydrogen, 2 Oxygen. Products have 4 hydrogen and 2 oxygen

    • What can we put in front of the the Hydrogen to balance the equation?

Types of Chemical Reactions

• Synthesis Reactions: Two or more substances combine to form a new substance

• Decomposition: One substance breaks up into two or more

• ​Displacement Reactions: One element replaces another in a compound

• Combu​stion Reactions: Release energy as heat and produces Carbon dioxide and water

Reaction Rates

• Balanced equations tell us what is involved in a reaction, but not what is specifically happening

• Reaction Rate: how quickly a chemical reaction takes place and for the concentration of reactants to products changes

  • Combination Reactions occur when atoms collide, and there are several ways to increase the collisions

    • Increase the amounts of reactants

    • Increase the temperature/kinetic energy

  • Separation reactions require the addition of energy

Catalysts

• Sometimes chemicals can influence a reaction without taking part in the reaction

• Catalysts: a substance that increases the speed a reaction by lowering the activation energy needed

  • It is not destroyed, but lowers energy and saves time and money​

Energy and Chemical Reactions

• When a reaction occurs, energy is either released or absorbed as heat

  • Exothermic reactions release heat​

  • Endothermic Reactions absorb heat​

• The energy either breaks or forms chemical bonds

  • The amount energy required to break a bond is Bond Energy​

    • Different bonds have different amount of bond energy

    • The amount of energy to form a bond is equal to the amount of energy to break that same bond

Multiple Choice

What fundamental Law of Chemistry is essential to balancing Chemical Equations

• Law of Mass Conservation

• Law of Gravity

• Law of energy

• The Law of Reactivity

Multiple Choice

This type of reaction results in two Compounds switching or "trading" one of their ions.

• Synthesis

• Decomposition

• Displacement

• Combustion

Multiple Choice

This type of reaction results in one reactant undergoing a change that results in two or more products

• Synthesis

• Decomposition

• Displacement

• Combustion

Multiple Choice

This type of reaction results in two or more reactants making one new substance

• Synthesis

• Decomposition

• Displacement

• Combustion

Multiple Choice

This type of reaction results in Heat, light, carbon dioxide and water as products

• Synthesis

• Decomposition

• Displacement

• Combustion

Acids and Bases

• Acids and bases are two groups of compounds that are corrosive

  • Acids are chemicals that give up Hydrogens in reactions

    • Tend to be sour

    • Form special ions called Hydronium Ion (H₃O⁺)

  • Bases are chemicals that loose hydrogen in reactions

    • Tend to be bitter and feel slippery

    • also called alkaline

    • Form Hydroxid ions (OH^-)

• When acids and Bases combine, they neutralize and form water and some form of ionic compound

  • Salt: an ionic compound (Not Just NaCl)​

Acidic, Basic, & Neutral Solutions

• When acids and bases are grouped, they use a scale that measures the Concentration of Hydronium ions to Hydroxide ions in a solution

• A solution with more Hydronium ions is Acidic

• A solution with more Hydroxide ions is Basic

• When a solution has an equal number of hydronium and hydroxide are equal, the solution is neither acidic nor basic and is called Neutral\

pH Scale

• The pH scale is a numerical scale that shows the acidity of a solution

  • Generally Goes from 1-14

  • pH values from 1-6: acidic

  • pH of 7: Neutral

  • pH of 8-14: Basic

• Calculated using the concentration

  • -log[H₃O]

Fill in the Blank

What is the pH of a solution where [H₃O] = 2.3 x 10^-2? (Round to two Decimal Places)

Fill in the Blank

What is the pH of a solution where [H₃O] = 6.3 x 10^-7? (Round to two Decimal Places)

Fill in the Blank

What is the pH of a solution where [H₃O] = 1.0 x 10^-2?