Matter and Energy Chapter 3

Transcription

1 Copyright 2004 by Houghton Mifflin Company. Matter and Energy Chapter 3 All rights reserved Matter Matter is the material the universe is composed of Matter has mass Matter occupies space Matter is classified in many ways, one of which is physical state Matter Physical states of matter: solid, liquid, gas State Keeps Keeps Compressible Flow Shape Volume Solid Yes Yes No No Liquid No Yes No Yes Gas No No Yes Yes 3

2 4 Characteristics of the substance under observation Properties can be either directly observable or the manner in which something interacts with other substances Physical Properties are those which can be observed without changing the composition of the sample Color, size, luster Density Chemical Properties are those which indicate the composition of the sample, and change as a result of the observation of these properties Flammability Reactivity 5 Classify each of the following as a chemical or physical property: The boiling point of water is 100 C. Diamond is very hard. Sugar ferments to form ethyl alcohol. 6

3 7 Physical Changes are changes to matter that occur without changing the composition of the sample State Changes boiling, melting, condensing Chemical Changes involve a change in the composition of the substance Produce a new substance Chemical reaction Classify each of the following as physical or chemical changes Iron is melted Iron combines with oxygen to form rust Sugar ferments to form ethyl alcohol Elements and Compounds Elements: substances which can not be broken down into simpler substances by chemical reactions Compounds: chemical combinations of elements Compounds are made of elements Compounds can be broken down into elements by chemical changes. Properties of the compound are not related to the properties of the elements that compose it A compound has the same chemical composition at all times 9

4 Mixtures & Pure Substances Pure Substances Can be elements or compounds Constant Composition - all samples have the same composition Have the same physical and chemical properties Homogeneous - same throughout the sample Separate into components (compounds) by chemical changes 3.4 Mixtures & Pure Substances Mixtures Variable composition Different samples may show different properties Separate into components based on physical properties All mixtures are made of pure substances Homogeneous or Heterogeneous Homogeneous: uniform throughout, appears to be one thing, Also called solutions Heterogeneous: non-uniform, contains regions with different properties than other regions Mixtures & Pure Substances Classify each of the following as a pure substance, a homogeneous mixture or a heterogeneous mixture. A glass of salt water A can of soda A stream with gravel on the bottom Copper metal 12

5 Separation of Mixtures Based on different physical properties of the components Distillation - different boiling points 3.5 Separation of Mixtures Based on different physical properties of the components Distillation - different boiling points Filtration - different physical states Energy, Temperature & Heat Energy is the capacity to do work chemical, mechanical, thermal, electrical, radiant, sound, nuclear Energy may affect matter raise its temperature, eventually causing a state change All physical changes and chemical changes involve energy changes 15

6 Energy, Temperature & Heat Heat is the flow of energy due to a temperature difference Exothermic: A process that results in heat being produced when a match is struck energy is produced as heat and light Endothermic: A process that absorbs energy melting ice to form liquid water absorbs heat 1 calorie (cal) is the amount of energy needed to raise the temperature of 1g of water by 1 C Joule: SI unit of energy J = 1 cal In nutrition, calories are capitalized and means kcal 1 Cal = 1 kcal 17 Convert 60.1 cal to joules 18

7 19 The amount the temperature of an object increases depends on the amount of heat (Q) added. If you double the added heat energy the temperature will increase twice as much. The amount the temperature of an object increases depends on its mass If you double the mass it will take twice as much heat energy to raise the temperature the same amount. Specific Heat (s) is the amount of energy required to raise the temperature of one gram of a substance by one C By definition, the specific heat of water is J/g C Table 3.2 Substance s (J/g C) Substance s (J/g C) Water liquid Aluminum solid 0.89 Water solid 2.03 Carbon solid 0.71 Water gas 2.0 Silver solid 0.24 Mercury liquid Gold solid 20 Amt of heat = (specific heat)(mass)(temp. change) Q = (s)(m)(δt) Calculate the amount of heat energy (in joules) needed to raise the temperature of 7.40 g of water from 29.0 C to 46.0 C 21

8 22 A 1.6 g sample of metal that appears to be gold requires 5.8 J to raise the temperature from 23 C to 41 C. Is the metal pure gold?