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
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A rusting car – a chemical oxidation/reduction reaction
Changes of Matter
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Fireworks – a complex set of chemical reactions including combustion
Changes of Matter
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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! (Can be tested)
- Experiment – Apply heat to ice; note the temperature when it melts; repeat many times
- Analyze data – Ice seems to melt at 0 °C
- Create theory – Ice melts at 0 °C! (comprehensive explanation)
A theory can become a law if the statement is reliably consistent and supported by an abundance of evidence.
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
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Practice – States
What takes up more space?
- A 500 g cube of ice
- A 500 g sample of water
- A 500 g sample of steam
Representing Matter
Macroscopic
Representing Matter
Particulate
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
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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
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Separation of Mixtures
Distillation
Separate salt from water by distillation
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Separation of Mixtures
Chromatography
Separate the components of a homogeneous mixture (purple) by passing the mixture through a medium where different substances (red and blue) move at different speeds.
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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
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.
Physical Properties of Matter
| Property |
Using the Property to Distinguish Substances |
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Is the substance colored or colorless? What is the color, and what is its intensity?
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Is it a solid, liquid, or gas? If it is a solid, what is the shape of the particles?
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At what temperature does a solid melt?
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At what temperature does a liquid boil (at 1 atm pressure)?
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What is the substance’s density (mass per unit volume)?
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What mass of substance can dissolve in a given volume of water or other solvent?
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Does the substance conduct electricity?
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How easily can a solid be deformed?
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How easily can a solid be drawn into a wire?
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How easily will a liquid flow?
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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?
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?
\[\begin{align*}
d &= \dfrac{m}{V} \longrightarrow \\[1.5ex]
m &= dV \\[1.5ex]
&= (0.95805~\mathrm{g~mL^{-1}})(1000~\mathrm{mL}) \\[1.5ex]
&= 958.05~\mathrm{g}
\end{align*}\]
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
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Conversions of Energy
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