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Matter & Its Changes

Holt – Chapter 1

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Chemistry

• 1. A physical science that studies the composition, properties, and interaction of matter.

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These Branches of Chemistrystudy …

• Organic – carbon compounds• Inorganic – non-organic substances• Physical – properties of matter, changes that occur

in matter & relationships between matter & energy• Analytical – identification of the composition of

materials• Biochemistry – living things• Theoretical – properties of new compounds by the

use of math and computers to design and predict

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Chemical Investigations

• Basic research – gaining knowledge about a particular topic (i.e., reactions of an element)

• Applied research – solves a particular problem (i.e., finding chemicals that do not cause depletion of ozone in the atmosphere)

• Technical development – applying useful ideas to solve problems (usually occurs long after basic research)

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Chemical Terms

• Mass – the measure of an amount of matter.• Matter – anything that has mass and takes up

space.• Atom – smallest unit of matter that retains the

properties of that matter.• Compound – formed by chemical bonding of 2

or more atom types

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MatterYes Can it be separated? No

Mixtures Pure Substances Is the Composition Can it be decomposeduniform? with chemical means?

Homogeneous Heterogeneous Compounds Elements Mixtures Mixtures (air, kool-aid) (blood, granite) (water, sugar) (H, Fe, U)

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Properties of Matter

• Physical – properties that can be measured without changing the identity of the substance (color, density, melting and freezing points)

• Chemical – relate to how a substance interacts with another substance to form a different substance

• Homogeneous Mixture – uniform composition (tea, solution)

• Heterogeneous Mixture – non-uniform composition (peanut butter)

• Pure substance – contains only 1 kind of substance (water)

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Matter Overview

• Matter is made up of either pure substances or mixtures.

• Pure substances can be compounds or elements which are both made up of atoms.

• Mixtures can be homogeneous (same throughout) or heterogeneous (different sized particles and substances)

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More on Properties

• Extensive – depends on the amount of matter present (mass, amount)

• Intensive – properties of a substance (boiling point, freezing point, density)

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Changes in Matter

• Physical – change of state or shape of a substance without the composition of the substance changing (ice melting)

• Chemical – involves the rearrangement of atoms of different elements in a substance and the formation of substances with different physical properties (baking a cake)

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Chemical Change or Reaction

One or more substances are converted into a different substance such as:

H + 0 H20

Reactants Product

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Energy and Chemistry

• Energy is either absorbed (ice melting) or released (liquid water freezing) in all chemical and physical changes.

• Energy is neither created nor destroyed; it changes form (chemical energy to light energy when fireworks explode)

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The following graph shows the relationship between temperature and heat energy

during the phase changes of water.

Energy in

Energy out

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Phases of Matter

• Highest Energy to Lowest• Plasma (many atoms have lost electrons)

• Gas• Liquid• Solid

• We will return to this topic when we get to Thermochemistry (heat)

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Periodic Chart Basics

• The elements are in atomic number (# of protons) order.

• Horizontal rows are called periods• Vertical columns are called families or groups

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More on the Periodic Table

• Elements in the same groups or families share similar chemical properties.

• In a period (row), elements close together tend to have similar properties. Going across a period, physical and chemical properties change somewhat regularly across a period then repeat in the next period. Elements in the same period are in the same horizontal row.

• A family or group of elements are in the same column.

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Metals

• Good conductors of heat and electricity• Can be hammered or rolled into thin sheets

(malleable)• (some) are easy to cut with a knife• Most are solids at room temperature• Can be drawn into strands of wire (ductile)• Have a shiny (metallic) luster• Have high boiling points

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Nonmetals

• Poor conductors of heat and electricity• Most are gases• Brittle as solids (break when pressure is

applied)• Have low boiling points

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Metalloids

• Have characteristics of both metals and nonmetals

• All are solids at room temperature

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Noble Gases

• Aka: Inert gases• Gaseous state at room temperature• Generally don’t react with other elements

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Get out old assignment:

• Let’s go over:• 22/19,21,24• 24/1,2• 25/all

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Thermal Chemistry (Heat Energy)

Energy is involved in chemical reactions.

Thermochemistry is the study of heat energy transfers in accompanying chemical reactions and physical changes.

Heat and temperature are NOT the same thing.

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• Heat – energy transferred from a hotter substance to a cooler substance.

• SI unit: joule j newton meter nm kilogram meter meter kgm2

second2 m2

Temperature – measure of the average kinetic energy of the particles of a substance or object.SI unit: degree oK, oC, K

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Temperature Conversion Equations

F = 9 C + 32 5C = 5 (F-32) 9K = C + 273

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• Convert 72 oF to oC• C = 5/9 (F-32)• C = 5/9 (72-32) = 22oC

• Convert -10 oC to oF• F = 9/5 C + 32• F = 9/5(-10) + 32 = 14oF

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Celsius to Kelvin: T = Tc + 273.15

Problem:

1. The lowest outdoor temperature ever recorded on Earth is -128.6 oF., recorded at Vostok Station, Antarctica, in 1983. What is this temperature on the Celsius and Kelvin scales?

Answers: -89.22oC, 183.93 K

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Specific heat capacity

The amount of energy that must be added to raise the temperature of a unit mass of a substance by one temperature unit.

• Units: J/g K• For Water: 4.180 J/g K• For Aluminum: 0.897 J/g K• Which one heats faster?

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/steel

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Heat Transfer Q = mCΔT = mC (Tf – Ti)

• Heat Transfer • q = mCΔT = mC (Tf – Ti)

• q, quantity of heat in joule• m, mass of substance in kg• c, specific heat for water in 4.186 j/g K• t, temperature in Celsius

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See table on frame 29.

Find the amount of heat needed to change the temperature of 5.0 g of liquid water from 8.0oC to 100oC.

q = mcDt = 5.0g(4.186 j/goC) (92oC) = 1.9 x 103 j

Again,

specific heat is the amount of heat necessary to change one kg of a substance 1 degree Celsius or Kelvin.

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• 12/3 When you turn on the hot water to wash dishes, the water pipes have to heat up. How much heat is absorbed by a copper water pipe with a mass of 2.3 kg when its temperature is raised from 20.0oC to 80.0oC?

• Q = mcDt• Q = (2.3kg)(1000g)(0.390J)(60.0oC)• kg goC• Q = 53820 J or 5.4x104J

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Law of Heat Exchange q lost = q gained

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• 0.300 kg of coffee, at a temperature of 95 °C, is poured into a room-temperature (20.oC) steel mug, of mass 0.125 kg. Assuming no energy is lost to the surroundings, what does the temperature of the mug filled with coffee come to?

• Applying conservation of energy, the total change in energy of the system must be zero. So, we can just add up the individual energy changes (the q's) and set the sum equal to zero. The subscript c refers to the coffee, and m to the mug.

• qc and qm•

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• tf = 91.8oC

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Latent Heat is energy transferred during phase changes

• Latent Heat• Crystalline materials change phase -- melt and freeze or vaporize and

condense -- at a single, fixed temperature.Energy is required for a change of phase of a substance. The ratio of the energy to the mass of the substance involved is called the latent heat of the substance. This is much like the specific heat we have just discussed. It is called latent heat because there is no change or difference in temperature.

•Latent heat of fusion Hf describes the heat necessary to melt (or freeze) a unit mass of a substance.

q = m Hf• Latent heat of vaporization Hv describes the heat necessary to vaporize

(or condense) a unit mass of a substance.

• q = m Hv•

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Temperature vs Heat

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Formulas

• Temperature change use: q = mc D t• Melting or freezing: q = m Hf

• Evaporation or Condensation: q = mHv

• Hf is latent heat of fusion, 3.33 x 102 J/g• Hv is latent heat of vaporization, 2.26 x 103 J/g• These values are for water.

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Problem

• A jar of tea is placed in sunlight until it reaches an equilibrium temperature of 32oC. In an attempt to cool the liquid to 0oC, which has a mass of l80 g, how much ice at 0oC is needed? Assume the specific heat capacity of the tea to be that of pure liquid water.

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m tea = 180g m ice = ? which is the mass of the water that has melted

c tea = c water = 4.186 J/goC

H f = 3.33 x 102 J/g and t final = 32oC

Q lost = Q gained tea loses and water gains only melting the ice

(mcDt)tea = (mHf)ice

m ice = (mcDt)tea

Hf ice

m ice = (0.180kg)(4.186 J/goC)(32oC)

3.33x102 J/g

= 7.2 x 10-2kg