Chemistry I

Chapter 1: Basic Concepts

What is…

Chemistry?

  • The scientific study of the composition, structure, and properties of matter as well as the changes in composition and energy that matter undergoes during reactions

Matter?

  • Anything that takes up space (has a volume)

Changes of Matter

A rusting car – a chemical oxidation/reduction reaction

Changes of Matter

Fireworks – a complex set of chemical reactions including combustion

Changes of Matter

Melting ice – a physical change

The Scientific Method

The careful, systematic approach to investigation

  • Question – Why does ice spontaneously melt outside?
  • Hypothesis – It’s too hot out!
  • Experiment – Apply heat to ice; note the temperature when it melts; repeat many times
  • Analyze data – Ice seems to melt at 0 °C
  • Draw conclusions – The melting point of ice is 0 °C!

Data

Data can be qualitative or quantitative.


Qualitative

This ice is cold!

This professor talks loudly.

Class lasts forever!

Quantitative

The ice is –4.8 °C.

This professor is outputting 78 db on average.

Class is 50 minutes long.

States of Matter

  • Solid, s – closely packed particles in regular patterns; has a fixed volume and shape; generally not compressible
  • Liquid, l – randomly arranged particles; adopt the shape of the container it is in; has a fixed volume; not very compressible
  • Gas, g – rapidly moving, far separated particles; adopts the shape of the container it is in; fills the container it in; no fixed volume; compressible
  • Aqueous, aq – a substance dissolved in water

States of Matter



Source: openStax

Practice – States

What takes up more space?

  1. A 500 g cube of ice
  2. A 500 g sample of water
  3. A 500 g sample of steam

Representing Matter

Macroscopic


A glass of water

Representing Matter

Particulate


A sea of water molecules

Source: Wikimedia

Representing Matter

Symbolic

\[\underbrace{\mathrm{H_2O}(l)}_{\mathrm{chemical~formula}}\]


  • An atom is the smallest particle of an element that retains the characteristic chemical properties of that element.
  • A molecule is a particle containing more than one atom held together by chemical bonds

Classifying Matter



Source: openStax

Mixtures

blend of two or more substances that preserve their identities

Homogeneous

uniform composition

  • Saltwater
  • Coffee
  • Air
  • Natural gas
  • Gasoline

Heterogeneous

not uniform

  • Salad
  • Soil
  • Cereal and milk
  • Ramen bowls
  • Car

Pure Substances

Element

  • H2(g)
  • Fe(s)
  • Na(s)
  • N2(s)
  • S8(s)

Compound

  • H2O(g)
  • Fe2O3(s)
  • NaCl(s)
  • NH3(g)
  • SO2(g)

Compounds

Law of Definite Proportions – a chemical compound always contains exactly the same proportion of elements by mass, regardless of the amount or source of the compound; also known as the Law of Constant Composition


Example: water (H2O) is always made up of 2 hydrogen atoms and 1 oxygen atom, and the ratio by mass is always approximately 11% hydrogen and 89% oxygen, no matter where the water comes from or how much water you have.

Compounds

Law of Multiple Proportions - whenever the same two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers.

Example: Carbon and oxygen form in a 1:1 ratio in carbon monoxide whereas carbon and oxygen form in a 2:1 ratio in carbon dioxide. They do not form in a weird ratio such as 1.346:1.

Separation of Mixtures

Filtration

Separate sand from water using a filter

Source: Wikimedia

Separation of Mixtures

Distillation

Separate salt from water by distillation

Source: Wikimedia

Separation of Mixtures

Chromatography

Separate the components of a mixture (purple) by passing the mixture through a medium where different substances (red and blue) move at different speeds.

Source: Wikimedia

Elements

Most elements involve a collection of single atoms, e.g. Fe(s)


Some are diatomic containing a covalent bond between pairs of atoms.


Br2(l), I2(s), N2(g), Cl2(g), H2(g), O2(g), F2(g)


“BrINClHOF”

Classification of Properties

Extensive

does depend on the amount of matter present

Intensive

does not depend on the amount of matter present

Classification of Properties

Physical

can be measured or observed without changing the chemical nature of matter

Chemical

describes the ability of a substance to undergo chemical change

Physical Properties of Matter

Property Using the Property to Distinguish Substances

Color

Is the substance colored or colorless? What is the color, and what is its intensity?

State of matter

Is it a solid, liquid, or gas? If it is a solid, what is the shape of the particles?

Melting point

At what temperature does a solid melt?

Normal boiling point

At what temperature does a liquid boil (at 1 atm pressure)?

Density

What is the substance’s density (mass per unit volume)?

Solubility

What mass of substance can dissolve in a given volume of water or other solvent?

Electric conductivity

Does the substance conduct electricity?

Malleability

How easily can a solid be deformed?

Ductility

How easily can a solid be drawn into a wire?

Viscosity

How easily will a liquid flow?

Density

Ratio of the mass of an object to its volume


\[\begin{align*} \mathrm{density} &= \dfrac{\mathrm{mass}}{\mathrm{volume}}\\[4ex] d &= \dfrac{m}{V} \end{align*}\]

Density of Water

What has a higher density, ice or water?

Temperature (°C)

Density (g cm–3)

0 (ice)

0.917

0 (liq water)

0.99984

2

0.99994

4

0.99997

10

0.9997

25

0.99707

100

0.95836


Ice floats in water.

Density of Water

Practice – Density

A 236.3 g sample of water completely fills a 237 mL (8 fl oz) bottle of water.

  • What is the density (in g mL–1) of the water?
  • What is the temperature (in °C) of the water?


\[\begin{align*} d &= \dfrac{m}{V} \\[1.5ex] &= \dfrac{236.3~\mathrm{g}}{237~\mathrm{mL}} \\[1.5ex] &= 0.997~\mathrm{g~mL^{-1}} \end{align*}\]

The density of water at 25 °C is 0.997 g mL–1.

Practice – Density

A pot of boiling water (at 100 °C) contains 1000 mL of water with a density of 0.95805 g mL–1.

  • What is the mass (in g) of the water?


\[\begin{align*} d &= \dfrac{m}{V} \longrightarrow \\[1.5ex] m &= dV \\[1.5ex] &= (0.95805~\mathrm{g~mL^{-1}})(1000~\mathrm{mL}) \\[1.5ex] &= 958.05~\mathrm{g} \end{align*}\]

Changes of Matter

Physical Changes

  • Changes in state where identity of substance is preserved

\[\begin{align*} \overbrace{\mathrm{H_2O}(l)}^{\mathrm{reactants}} &\longrightarrow \overbrace{\mathrm{H_2O}(g)}^{\mathrm{products}} \\[1.5ex] 1.0~\mathrm{g} ~~ &\longrightarrow ~~ 1.0~\mathrm{g} \end{align*}\]

Law of Conservation of Mass - mass is neither created nor destroyed; it is conserved

Changes of Matter

Chemical Changes

  • Identity of substance is not preserved

\[\begin{align*} \overbrace{2\mathrm{H_2}(g) + \mathrm{O_2}(g)}^{\mathrm{reactants}} &\longrightarrow \overbrace{\mathrm{2H_2O}(g)}^{\mathrm{products}}\\[1.5ex] 4.04~\mathrm{g} ~ + ~ 32~\mathrm{g} ~~ &\longrightarrow ~ 36.04~\mathrm{g} \end{align*}\]


Mass is conserved.

Energy

Energy is the capacity to do work

  • Kinetic Energy – energy associated with motion
    • Mechanical – mass in motion (car, ball, etc.)
    • Thermal – the motion of particles (atoms, molecules, etc.)
    • Electrical – movement of electrons in a conductor
  • Potential Energy – energy associated with an object’s state or position
    • Mechanical – mass at rest
    • Gravitational – a counterweight held in the air
    • Chemical – energy stored in chemical substances
    • Electrostatic – associated with the separation of charges

Law of Conservation of Energy - energy is neither created nor destroyed, only transformed; the energy of the universe is constant

Conversions of Energy

Source: Wikimedia

Conversions of Energy

Source: Wikimedia