south texas college

CHEM 1405 Course Guide

States of Matter


There are three phases that are made up of microscopic particles and all of them behave differently from each other.

  • Solids: Are tightly packed together and vibrate, but they do not move from place to place
  • Liquids: Are close together, but do not have a regular arrangement. They vibrate and are able to move about
  • Gases: Are well separated, vibrate, and move freely at high speeds

Condensed states of matter: Liquids and solids

Characteristics and Explanations of Solids, Liquids, and Gases
State of Matter Characteristic Explanation
Solid Retains a fixed volume and shape Rigid - The particles lock into place
  Not easily compressible Little free space between particles
  Does not flow easily Rigid - The particles cannot move/slide past each other
Liquid Assumes the shape of the container which it occupies Particles move/slide past each other
  Not easily compressible Little free space between particles
  Flows easily Particles can move/slide past each other
Gas Assumes the shape and volume of the container Particles can move past each other
  Compressible Lots of free space between particles
  Flows easily Particles can move past each other

For a fun, interactive simulation to help you get a better understanding of the states of matter, visit PhET Interactive Simulations by the University of Colorado Boulder.

Temperature & Density

There are three systems of measurement widely used for temperature:

  • Celsius scale - used in physical sciences
  • Kelvin scale - used in physical sciences
  • Fahrenheit scale - used in many engineering sciences

Note: The size of the temperature unit (degree) is the same for Kelvin and Celsius scales. The difference is the zero points.

Conversions:

Temperature (Kelvin) = temperature (Celsius) + 273.15

or

Temperature (Celsius) = temperature (Kelvin) - 273.15

Example:
Convert 400.0 K to the Celsius scale.

400.00 K - 273.15 = 126.85 °C

Helpful Tip:
Kelvin does not use a degree symbol for its unit unlike Celsius and Fahrenheit; it is symbolized by the letter K.

The degree size and zero points are different when considering Fahrenheit. As seen in the illustration above, The degree size for Fahrenheit is 180° and 100° for Celsius. So, the unit factor is:

180 °F                                                9 °F  
-------                       or                       -------
100 °C                                               5 °C  

This is because 180 ÷ 100 = 1.8 and in fraction form that is 9/5. You will also have to use the reciprocal depending on the direction that is needed.

Now, for the difference in zero points. To obtain the temperature in Celsius, you must subtract 32 °F from the given temperature in Fahrenheit and then multiply the unit factor to adjust for the difference in degree size.

                5 °C
(TF - 32 °F) X ------- = TC
                9 °F
As you can see in this equation, the reciprocal was used.

If the degree is needed in Fahrenheit and you have Celsius, then the following equation is used.

    9 °F
TF = TC X ------- + 32 °F
    5 °C

Example:
Convert 98.6 °F to the Celsius and Kelvin scales.

First, convert to Celsius:

               5 °C
(98.6 °F - 32 °F) X ------- = 37.0 °C
               9 °F

Next, convert the Celsius answer you just obtained to the Kelvin scale:

TK = TC + 273.15
TK = 37.0 °C + 273.15
TK = 310.2 K

Density: A property of matter used as an "identification tag" for a substance - the mass of the substance per unit volume of the substance.

               mass
Density = -------------
                volume

Names and Densities of Liquid Compounds
Compound Density in g/cm3 at 20 °C
Chloroform 1.492
Diethyl ether 0.714
Ethanol 0.789
Isopropyl alcohol 0.785
Toluene 0.867


Example:
Identify the unknown liquid. 25.00 cm3 of the substance has a mass of 19.625 g at 20 °C. Use the chart on the right to solve for what the unknown liquid could possibly be.

The first thing needed, is to find the density of the unknown liquid:

mass               19.625 g             
Density = ------------- = ----------------------- = 0.7850 g/cm3
volume             25.00 cm3               

The density obtained matches with the density of isopropyl alcohol.
Note: Ethanol is also very close and you would need to run more tests in order to ensure that isopropyl alcohol is the correct unknown liquid. 

Densities of Various Common Substances at 1 atm of pressure & 20 °C
Substance Physical State Density (g/cm3)
Oxygen Gas 0.00133
Hydrogen Gas 0.000084
Ethanol Liquid 0.789
Benzene Liquid 0.880
Water Liquid 0.9982
Magnesium Solid 1.74
Salt (sodium chloride) Solid 2.16
Aluminum Solid 2.70
Iron Solid 7.87
Copper Solid 8.96
Silver Solid 10.5
Lead Solid 11.34
Mercury Liquid 13.6
Gold Solid 19.32

 

 

FUN FACTS:

The liquid in your car's lead storage battery changes density when the sulfuric acid is consumed as the battery discharges. If the battery falls below a certain amount, the battery will have to recharge.

 

You can determine the amount of antifreeze, which tells you the level of protection against freezing in the cooling system of your car.

 

The center of a black hole (the singularity) is infinitely dense.

 

Saturn has the lowest density of all the planets in our solar system. Saturn has a density of 0.687 g/cm3 which is less than water. So, if you have a large enough pool filled with water, Saturn will float!

Silver has a density of 10.5 g/cm3 and gold has a density of 19.3 g/cm3. Which would have a greater mass, 5 cm3 of silver, or 5 cm3 of gold?

Silver:

               mass
density = -------------
                ​volume

mass = density X volume
= (10.5 g/cm3) X (5 cm3)
mass = 52.5 g

Gold:

mass = (19.3 g/cm3) X (5 cm3)
mass = 96.5 g

Answer: gold has more density.

One of the body's responses to an infection or injury is to elevate its temperature. A certain flu victim has a body temperature of 102 °F. What is the temperature on the Celsius scale?

Converting °F to °C

                5 °C
(TF - 32 °F) X ------- = TC
                9 °F

              5 °C
(102 °F - 32 °F) X ------- = 38.9 °C
               9 °F

Answer: 38.9 °C

An irregularly shaped stone was lowered into a graduated cylinder holding a volume of water equal to 2.0 mL. The height of the water rose to 7.0 mL. If the mass of the stone was 25 g, what was its density?

You must find the difference in the volume of water from the initial point to after the stone was dropped.
So, subtract 7.0 mL from 2.0 mL to obtain 5.0 mL, then plug it into the equation.

  25 g
density = ------- = 5 g/mL
  5 mL

Answer: density = 5 g/mL

Convert -196 °C to the Kelvin scale.

Temperature (Kelvin) = temperature (Celsius) + 273.15
= -196 °C + 273.15
TK = 77 K

Answer: TK = 77 K

Specifics

Please note that at 2:15, the question being asked isn't complete until after the answer is provided.

Heat capacity: The amount needed to raise the temperature of an object 1ºC. This depends on mass and composition.

Example:
It will take more heat to increase the temperature of a large pot of water than a small cup of water.
It will take more heat to increase the temperature of water than it will metal.

Comprehension Question:
Which has a higher heat capacity; water or gold? (Highlight box to reveal answer)

Water will have a higher heat capacity.
Gold (a metal) is a good conductor of heat and would have a lower specific heat.

Specific Heat Capacity (C): The amount of heat it takes to raise the temperature of 1 g of a substance 1°C.

          q              cal or J
C = ------------- = -------------------
           mΔT          g (°C or K)

Please note: The temperature units for these are Kelvin
   
   
   
   
   
   
   
   
   
   
   
   

 

In this video by Melissa Maribel, you will learn how to figure out the heat and specific heat capacity in two common calorimetry problems.