Notes, summaries, assignments, exams, and exercises for Chemistry for Secondary education

Classification of Matter: Pure Substances and Mixtures

Pure Substances

Substances that are formed by the same kind of particles (molecules, atoms, etc.).

• Elements: Formed by the same kind of atom. They cannot be divided by chemical means. Examples: Phosphorus (P), Oxygen (O), Carbon (C).
• Compounds: Formed by the same kind of molecules. They can be divided chemically. Examples: Water (H₂O), Carbon Dioxide (CO₂).

Mixtures

Substances that are formed by different kinds of particles.

• Homogeneous (Solutions): The different components cannot be visually distinguished. Example: Seawater.
• Heterogeneous: The different components can be visually distinguished. Example: Granite.

1. Defining the Atom

The atom is the smallest unit of a chemical element that retains...

Properties and Classification of Mixtures

A mixture is the aggregation of matter of two or more substances that meet the following conditions:

• a) The characteristic properties of the components are not altered.
• b) The amount or proportion of each component can be variable.
• c) The components can be separated by physical methods (evaporation, filtration, magnetism, etc.).

Homogeneous and Heterogeneous Mixtures

A mixture is homogeneous when its components cannot be distinguished at a glance because it has the same appearance throughout. A mixture is heterogeneous when the components can be appreciated by the naked eye.

Physical and Chemical Processes

In a physical process, there are no alterations to the substances that intervene. For example, filtration...

Properties of Matter

Characteristic and General Properties

There are some characteristic properties which allow us to identify substances (e.g., density, conductivity, color) and some general properties common to all types of matter (e.g., mass, volume, temperature).

Pure Substances

Types of Pure Substances

A pure substance is a form of matter with a constant composition that does not change regardless of physical conditions. Pure substances are categorized into two main types:

Compounds

Compounds are pure substances that can be chemically decomposed into simpler substances.

Elements

Elements are pure substances that cannot be decomposed into simpler substances by any chemical or physical procedure.

Examples of Pure Substances

• Compounds: Distilled water,

Fundamentos da Termodinâmica

O Que é Calor?

Calor é a grandeza física que mede a energia térmica que passa de um corpo para outro devido à diferença de temperatura entre eles.

Definição de Caloria

Caloria: É a quantidade de calor necessária para elevar a temperatura de 1g de água de 14.5 ºC para 15.5 ºC.

Calor Sensível e Calor Latente

Calor Sensível: Ocorre quando há apenas mudança de temperatura. Ex: aquecimento de um metal.

Calor Latente: Ocorre quando há mudança de estado físico e não de temperatura. Ex: derretimento do gelo.

Calor Específico das Substâncias

Calor Específico: Diferentes substâncias necessitam de quantidades distintas de calor para um aumento de 1 ºC. Ex: Ferro (Fe) = 0.11 cal/g°C. Isso significa que para...

Dynamic Equilibrium and System Properties

1. Dynamic Equilibrium (⇄): This is a dynamic, not static, state. Temperature relates to the speed of molecules. Concentration formulas include C = n/v, n = C * v, and v = n/C.

• Rate: The rate of the forward reaction equals the rate of the reverse reaction.
• Concentration: Concentrations remain constant at equilibrium, though they are not necessarily equal.
• Molecules: Molecules are destroyed and created at the same speed.
• System Type: Must be a closed system where no matter flows in or out. It requires constant temperature (no phase change, color change, or pressure change).

Inert Gases and Catalysts

• Inert Gases: Adding an inert gas (e.g., Ar, He) results in no shift in equilibrium.
• Catalysts: Adding a catalyst

Construction of CO, LASER
* It is basically a discharge tube having cross sectional area 1.5 mm? And length 260 mm. The discharge tube is filled with active medium (mixture of gases) carbon dioxide, nitrogen and helium in 1 : 4 : 5 proportions respectively. The active centers are CO, molecules lasing on the transitions between the vibrational levels of the electronic ground state.
* The terminals of the discharge tubes are connected to a D.C. Power supply.
* The ends of the discharge tube are fitted with NaCl Brewster windows so that the laser light generated will be polarized.
* Two concave mirrors one fully reflecting and the other partially form an optical resonator.
* The active medium is a gas mixture of COz, N2 and He. The laser transition...

Understanding Temperature

What is Temperature?

Temperature is the measurement of a substance's thermal energy.

Measuring Temperature

Mercury Thermometer

A mercury thermometer consists of a bulb containing liquid mercury and a thin tube. The liquid expands due to thermal expansion and rises up the tube, allowing the temperature to be read on a calibrated scale.

Digital Thermometer

A digital thermometer uses a microprocessor that measures the temperature and displays it on a liquid crystal display (LCD).

Temperature Scales

Common temperature scales include Celsius (ºC) and Kelvin (ºK).

• Celsius to Kelvin: K = C + 273.15
• Kelvin to Celsius: C = K - 273.15

Heat Transfer Mechanisms

Conduction

Conduction is the transfer of heat energy primarily from solid to solid...

Ionic Bonds

Ionic bonding is a type of chemical bonding that involves the electrostatic attraction between oppositely charged ions. Ionic bonds form when a metal and a non-metal exchange electrons. Positive ions are called cations and negative ions are called anions.

Ionic Substances

All ionic compounds form crystals that consist of lattices of positive and negative ions packed together in a regular way. The lattice is held together by the strong electrostatic attractions between the ions. Ionic compounds form crystals because the ions are arranged in a regular and repeated pattern, known as a Giant Ionic Lattice.

Properties of Ionic Substances

• High Melting and Boiling Points: Ionic bonds are very strong. Significant energy is required to break

Chemical Energy and Molecular Bonds

Chemical energy is the energy associated with chemical bonds and intermolecular attraction. The chemical energy of a set of reacting substances changes since bonds break and form new bonds, creating new products.

We call the energy exchanged in the form of heat between a system containing a chemical reaction and its surroundings the heat of reaction.

Exothermic and Endothermic Reactions

• Exothermic Reaction: The energy of the reactants is greater than that of the products and has a negative sign (e.g., combustion). These reactions release chemical energy via heat.
• Endothermic Reaction: The energy in the system grows. The exchange of energy via heat goes from the surroundings toward the system, so the heat of reaction

• Metal + nonmetal = ionic bond

•  Nonmetal + nonmetal = covalent bond  

•  Metal + metal = metallic bond

• Electron filling pattern: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f

• Physical Changes

  • Do not create a new substance.

• Chemical Changes - Do produce new substances.

•  Ions - Atoms can gain or lose electrons to form ions (atoms with a charge. 

• • Anion - Atom with a negative charge. 

• • Cation - Atom with a positive charge.
  

• quantitative= number/amount, qualitative= observation of physical change
  

• alkali metals the column of elements from lithium to francium.
  

• Alkaline earths the column of elements from beryllium to radium.
  

• Halogens the column of elements from fluorine to astatine.
  

• The Periodic Law states that the physical and