Experiment 4
Changes in Matter
Properties of Substance:
Each substance has a set of properties that are characteristic of that substance and give it
a unique identity.
Properties – the “personality traits” of substances
2 Main types of Properties:
a. Physical properties
- Inherent characteristics of a substance which can be determined without altering its
composition.
- Properties perceived by the senses and those that can be measured by physical means.
- Tells what a substance is.
Types of Physical Properties:
1. Intrinsic property
- Properties that are characteristic of any sample of a substance regardless of the
amount, size or shape.
- Examples: taste, odor, color, physical state, viscosity, hardness, solubility in water,
boiling point, melting point, freezing point, specific heat, texture, refractive index,
tensile strength and density.
2.
-
Extrinsic property
Properties that are not characteristic of the substance itself.
Those that vary with the change in amount, size or shape.
Example: size, shape, length, width, height, volume and weight.
b. Chemical properties
- Properties which make it possible for a substance to form new substances either by
reacting alone or with other substances.
- Tells what a substance does.
- Example: stability towards heat, stability towards light, susceptibility to oxidation,
reactions with water and other susceptible substances.
Matter can undergo 2 Types of Changes:
1.
-
Physical change
Any change not involving a change in the substance’s chemical identity
It occurs when objects undergo a change that does not change their chemical nature.
Physical properties can be observed without changing the composition of matter.
Ways to determine Physical Change
A. Change in States
a. Sublimation – passage of molecules from solid to gaseous state
b. Deposition – passage of molecules from gaseous to solid state
c. Condensation – passage of molecules from gaseous to liquid state
d. Evaporation – passage of molecules from liquid to gaseous state
e. Freezing – conversion of liquid to solid
f. Melting – transition of solid to a liquid
g. Boiling – transition of liquid to gas
B.
C.
D.
E.
Change in shape - drawing copper into a wire, heating glass tubing
Mixing of two substances (may be in two states) - salt and water
Breaking of a solid - breaking of glass
Change in size (expansion)
2. Chemical change
1. Alter the composition of a substance
2. Tends to react chemically to produce new substances that have different composition
and properties.
3. Process in which one set of substance (reactant) is transformed into a new set of
substances (products)
Ways to determine chemical change:
1. Change in odor
2. Change in color
3. Change in temperature or energy
a. Exothermic
b. Endothermic
4. Change in form
5. Light, heat and sound is given off
6. Formation of gases, often appearing as bubbles
7. Formation of precipitate (insoluble particles)
8. Decomposition of organic matter
Different Types of Chemical Change:
1.
2.
3.
4.
5.
6.
7.
8.
Synthesis
Precipitation
Decomposition
Neutralization
Single Displacement
Double Displacement
Combustion
Reduction – Oxidation Reaction
Physical or Chemical Changes of Some Common Process
Process Taking Place
Type of Change
Accompanying
Observations
Rusting of iron
Chemical
Shiny, bright metal changes
to reddish-brown rust
Burning of sulphur in air
Chemical
Yellow, solid sulphur
changes to gaseous, choking
sulphur dioxide
Boiling an egg
Chemical
Liquid white and yolk
change to solid
Combustion of gasoline
Chemical
Liquid gasoline burns to
gaseous carbon monoxide,
carbon dioxide and water
Digesting food
Chemical
Food changes to liquid
nutrients and partially solid
waste
Burning wood
Chemical
Wood burns to ashes,
gaseous carbon dioxide and
water
Boiling of water
Physical
Liquid changes to vapour
Sawing of wood
Physical
Smaller pieces of wood and
sawdust are made from a
larger piece of wood
Heating of glass
Physical
Solid becomes pliable
during heating and the glass
may change its shape
Experiment 5: Endothermic and Exothermic Reactions
When a chemical reaction happens, energy is transferred to or from the surroundings and often
there is a temperature change. For example, when a fire burns it transfers heat energy to the
surroundings. Objects near a fire become warmer and the temperature rise can be measured with
a thermometer.
Exothermic and endothermic are terms that describe the change of heat during a reaction.
Exothermic reactions release heat because the energy of the system has dropped, so the excess
energy is left as heat. This will cause a steady increase in temperature in the beginning of the
reaction until most the reactants have reacted. Endothermic implies heat is taken in by the
reaction because the energy of the system has increased. This will create a steady drop in
temperature.
Exothermic reactions release heat because the products are less energy than the reactants. Heat
accounts for this extra energy and can be identified by a rising temperature. Endothermic
reactions get cold because energy is needed to form the products, which are higher energy than
the reactants. Usually energy is needed to break bonds and energy is released when bonds form.
Baking soda combined with citric acid requires energy, or is endothermic, so the temperature
should decrease. Baking soda combining with different compounds causes different bonds to
break and reform, which is what causes the temperature fluctuations in the different
reactions.
Exothermic reactions
These are reactions that transfer energy to the surroundings. The energy is usually transferred as
heat energy, causing the reaction mixture and its surroundings to get hotter. The temperature
increase can be detected using a thermometer. Some examples of exothermic reactions are:
• Burning ( combustion)
• neutralisation reactions between acids and alkalis, and
• the reaction between water and calcium oxide
Endothermic reactions
These are reactions that take in energy from the surroundings. The energy is usually transferred as
heat energy, causing the reaction mixture and its surroundings to get colder. The temperature
decrease can be detected using a thermometer. Some examples of endothermic reactions are:
• the reaction between barium hydroxide and ammonium chloride
• the reaction between ethanoic acid and sodium
https://chemicalparadigms.wikispaces.com/file/view/General+Chemistry+Unit+5+Energetics_Jan
+2010.pdf
Endothermic reaction: H3C6H5O7(aq) + 3NaHCO3(s)  3CO2(g) + 3H2O(l)+NaC6H5O7(aq)
Exothermic reaction: 2Zn + 2HCl  2ZnCl + H2
https://chemicalparadigms.wikispaces.com/file/view/General+Chemistry+Unit+5+Energetics_Jan
+2010.pdf
http://www.chem.ufl.edu/~saacs/outreach/tempprobes.pdf
The energy contained in chemical bonds that can be converted into heat is known as enthalpy
and is given the symbol H. It is impossible to measure the actual heat content or enthalpy of a
particular substance, but what can be readily measured is the enthalpy change for a reaction, ΔH.
For exothermic reactions the heat content (enthalpy) of the products is less than that of the
reactants. By convention the enthalpy change for the reaction, ΔH, is said to be negative (–). For
endothermic reactions, where the enthalpy of the products is more than the enthalpy of the
reactants,the enthalpy change, ΔH, will have a positive value (+). Note that the plus and minus
symbols indicate the direction of heat flow; they do not imply positive or negative energy.