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					Unit 5: Conservation of Mass as
 an Example of a Fundamental
             Core 270
            Spring 2008
       Dr. Sharon Fredericks
                Matter and mass
• Matter

• Mass = measure of the amount of matter; relies on
  inertia (resistance to changing velocity)
   – Units: gram or kilogram, slug
• Weight = depends on the strength of gravitational
  force; technically not the same as mass but ok for us
   – Units1: Newton, pound
• An astronaut’s weight changes as he/she goes from
  Earth to the moon, but her/his mass doesn’t.
• Close to the Earth, 1 kg of something has a weight of
  2.2 lb
               Studying Matter
• Properties
  – Size, color, temperature
  – Chemical composition: what matter is made of
  – Chemical reactivity: how matter behaves
• Transformations
  – Physical change: one that does not alter the
    ___________________make-up of a substance
     • Phase change (melting, freezing, evaporating),
  – Chemical change: one that does alter the
    ___________________ make-up of a substance
     • New substance is formed
             Physical   Change 2

Figure 2.2
Chemical         Change 2

    Figure 2.5
         What do you think?
• In the boxes below, each solid circle
  represents an atom of the same element. Each
  hollow circle represents an atom of a 2nd
• The transformation from left to right is best
  viewed as a chemical change or physical
  change? Why?
             Sample problem
Identify which are chemical changes and which are
  physical changes:
• Mixing salt and water to make salt water
• Steam condensing to water
• Milk souring
• Ignition of matches
• Breaking of a dinner plate
• Leaves turn red in Autumn
               States of Matter
• 2 broad categories: solid & fluid
   – Solid:

   – Fluid:

• Conversion of one state to another is called
• Solid    Liquid = melting/freezing
   – Melting point = freezing point
• Liquid      Gas = boiling/condensing
   – Boiling point = vaporization temperature
• Solid       Vapor = subliming/condensing
• Liquid      Vapor = evaporating/condensing
                    Changes of                Phase 2

Heat is added in order to pull atoms or molecules a part for melting & evaporation.
Heat is released during freezing and condensation as atoms & molecules “bond”.
              Sample Problem
• Sulfur dioxide (SO2) is a compound produced when
  sulfur burns in air. It has a melting point of –72.7oC
  and a boiling point of –10oC. In what state does
  SO2 exist at room temperature (25oC)? How about
  at –11oC?
            Solution to Problem
• Note that the scale is in Celsius and both the mp and
  the bp are negative numbers
• As you go to the left, you increase in the negative
               Your Turn
• The melting point of the element bromine is
  –7.2 oC. Its boiling point is 58 oC. In what
  state does Br2 exist at room temperature
  (25oC)? How about at –11oC?
            Solution to Problem
• Note that the scale is in Celsius.
• The mp is negative; the bp is positive. So zero degrees
  Celsius is somewhere in between.
• As you go to the left, you increase in negative
  numbers. As you go right, you increase in the positive
          Melting vs. Dissolving
Melting                        Dissolving
• Involves a solid to liquid   • One substance is mixed
  transition at a specific       with another to form a
  temperature.                   solution
• Only ONE substance (no
  solvent)                     • At least TWO substances
• Ice  water at 0 degrees
  C                            • Salt + water salt water
• Sugar(s) molten sugar         at all temperatures above
  at 365 degrees F (186 deg      room temperature
  C)                              – Aqueous solution
            Sample Problem
• What is happening     • What is happening
  when you put an ice     when you put a sugar
  cube in your mouth?     cube in your mouth?
         Conservation of Mass
• It is Fundamental Law

• To be tested, the type of system has to be
  determined1: closed or open
• Closed: matter can not enter or leave the system;

• Open: Matter can enter and leave the system; most
  systems are open
           Concept Problem
A piece of dry ice (solid carbon dioxide) is
  placed in an air-tight container and sealed
  shut. At room temperature, the solid
  changes to a vapor or sublimes.
Is the mass of the carbon dioxide and
  container the same, less, or more after all
  the solid evaporates?
 Closed and Open Systems with
        respect to matter
• Closed
  – Sealed glass bottle
  – Closed zip-lock bag
• Open
  –   A room with an open window or door
  –   Car
  –   Ocean, sea, lake, pond, river
  –   Anything in which matter (remember gases like air) can
      flow in and out
                 The    Earth1

• It can be considered an open system because we
  know that material from space can fall to Earth.
  Furthermore, the space shuttle, rockets, etc can
  leave and sometimes return
• It can be considered a closed system for all
  intensive purposes because a fraction of 1% of
  matter is crossing the boundary.
• This is a good ___________________________
  and demonstrates that sometimes we settle for a
  description or law that is ___________________
Law of Conservation of Mass for
       an Open System
• mfin = mori + min – mout
   –   mfin = total matter in final condition of system
   –   mori = total matter in original condition of system
   –   min = matter that has been put into the system
   –   mout = matter that has been taken out of the system

• If Dm = min – mout        then

• If morig is constant, then
• Rearranging:
• By tracking changes,
• A person has a checking account balance of
  $515.20. He took out $80 from the ATM, which
  he used for daily expenses. He bought $35.90
  worth of groceries using his debit card (from
  checking) and paid his Visa bill ($52.88) and rent
  ($400). He deposited his weekly paycheck of
  $350. What was mori, min, mout, Dm, and mfin?
  Assume the amount of money=mass and use the
  formulas introduced.
                 Your Turn
A candy factory made 100 dozen chocolate truffles. It sent
  30 dozen to the local candy store, 45 dozen to the candy
  store in the next town, and shipped out 4 dozen to a private
  customer. It placed the rest in its own factory store. The
  factory store sold 6 dozen during the first week of sales,
  but the private costumer sent back a dozen because she
  only wanted 3 dozen.
What was the original amount (morig), the amount of candy
  that left the factory (mout), the amount of candy that came
  into the factory (min), the change of amount (Dm), and the
  final amount (mfin) of candy in the factory?
          Exception to the law3
• In ____________________reactions, mass is not
  conserved and is converted to energy according to
  Einstein’s famous equation E=mc2.
• In ________________________reactions mass is
  conserved, since in every case the mass-energy of
  the reactants is huge in comparison to the energy
  absorbed or released when they react.
   – “By way of example, a gram of TNT releases 4.16 kJ of
     energy when exploded. However, the rest-energy of a
     gram of TNT is 90 TJ, or about 20 billion times as
     much. This means that even if the products of a TNT
     explosion were stopped and allowed to cool to the
     original temperature, they would only lose 1 part in 20
     billion in weight. This amount would be very difficult
     to measure.”3
      Amalie (Emmy)             Noether 1

• Brilliant mathematician – considered one of the
  most important in the 20th century
• Established role of symmetry to laws of
  conservation with respect to the General Theory of
• Could not officially teach in universities in
  Germany and was given a token salary after 10
• Could not present any of her original work,
  including a ground breaking paper – a male
  colleague took her place
1. Kelinsteuber, et al., Natural Science 5th
   edition, King’s College, PA, 2004.
2. Suchocki, J., Conceptual Chemistry, 2nd
   edition, Benjamin Cummings, 2004.
3. Wikipedia web site:

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