Chapter 4 Properties of Matter

Chapter 4
Properties of Matter
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4.1 Properties of substances
properties – characteristic of the substance and
give it a unique identity
physical properties – inherent characteristics of
a substance
chemical properties – the ability of a substance
to form new substance either by reaction
or by decomposition
ex. chlorine Cl 2
• not burn but will support the combustion
of other substances
• used as bleaching agent
• combine with Na to form salt
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4.2 Physical changes
changes in physical properties or changes in the
state of matter without changing in composition
ex. ice melting
water boiling
Pt wire is heated in a burner flame, color
changes from silvery metallic to glowing
red
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4.3 Chemical changes
new substances are formed that have different
properties and composition from the original
material
ex. 1.000 g copper + 0.251 g oxygen
1.251 g copper(II) oxide
ex. water can be decomposed chemically into
hydrogen and oxygen
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chemical equation – a shorthand method for
expressing chemical changes
electrical
2 H 2 O 2 H 2 + O 2
energy
Δ
2 Cu + O 2 2 CuO
reactant product
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4.4 Conservation of mass
law of conservation of mass – no change is
observed in the total mass of the substances
involved in a chemical reaction
mass of reactants = mass of products
ex. water hydrogen + oxygen
100.0 g 11.2 g 88.8 g
100.0 g
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4.5 Energy
energy is the capacity of matter to do work
exists in many form: mechanical, chemical,
electrical, heat, nuclear, radiant or light energy
matter can have both potential and kinetic energy
potential energy (PE) – stored energy
kinetic energy (KE) – energy that matter
possesses due to its motion
energy can be converted from one form to another
mechanical energy
electric generator
> 90% efficiency
electrical energy
solar energy
~ 15% efficiency
electrical energy
in chemistry, energy is most frequently expressed
as heat
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4.6 Heat: quantitative measurement
SI unit of energy: joule (J)
4.184 J = 1 cal (calorie)
1 calorie – the quantity of heat energy required to
change the temperature of 1 g of water by
1 o C (from 14.5 o C to 15.5 o C)
kilocalorie (kcal) kilojoule (kJ)
heat capacity – the quantity of heat required to
change the temperature of 1 g of the
substance by 1 o C
mass of specific heat
Δt= heat
substance of substance
raise the temperature of 200 g of water by 10 o C,
the amount of heat needed
(200 g)(4.184 J/g o C)(10 o C) = 8.37 × 10 3 J9

ex. 4.1 If 1638 J raise the temperature of 125 g
of the solid from 25.0 o C to 52.6 o C,
calculate the specific heat in J/g o C.
heat 1638 J
specific heat = ──── = ─────────
g × Δt (125 g)(52.6 – 25) o C
= 0.475 J/g o C
ex. 4.2 a metal with a mass of 212 g is heated
to 125.0 o C, and then dropped into 375 g
water at 24 o C. the final temperature of
water is 34.2 o C. specific heat of metal
heat gain by water = (375 g)(10.2 o C)(4.184J/g o C)
= 1.60 × 10 4 J
heat
1.60 × 10 4 J
specific heat = ──── = ─────────
of metal g × Δt (212 g)(125 – 34.2) o C
= 0.831 J/g o C
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4.7 Energy in chemical changes
in chemical changes, matter either absorbs or
releases energy
• electric energy produced in lead storage battery
• light energy in light stick
• heat and light are released from combustion of
fuels
• electrical energy is used in electroplating of
metal
• radiant energy is used by green plants in
photosynthesis
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4.8 Conservation of energy
• electrolysis of water
electrical energy is absorbed
products have higher potential energy
• hydrogen is burned in O 2
energy is released
product has lower potential energy
Law of conservation of energy –
energy can be neither created nor destroyed,
though it can be transformed from one to another
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