Matter and Energy. Chapter 3

Transcription

1 Matter and Energy Chapter 3 1

2 Universe Classified Matter is the part of the universe that has mass and volume Energy is the part of the universe that has the ability to do work Chemistry studies The properties of different types of matter The way matter behaves when influenced by other matter and/or energy 2

3 Changes in Matter Physical Changes do not change the fundamental components that make the substance State Changes boiling, melting, condensing Chemical Changes involve a change in the fundamental components of the substance Produce a new substance Chemical reaction Reactants Products 3

4 Classify Each of the following as Physical or Chemical Properties The boiling point of ethyl alcohol is 78 C. Diamond is very hard. Sugar ferments to form ethyl alcohol. 4

5 Classify Each of the following as Physical or Chemical Properties The boiling point of ethyl alcohol is 78 C. Physical property describes inherent characteristic of alcohol boiling point Diamond is very hard. Physical property describes inherent characteristic of diamond hardness Sugar ferments to form ethyl alcohol. Chemical property describes behavior of sugar forming a new substance (ethyl alcohol) 5

6 States of Matter solid, liquid, gas State Shape Volume Compress Flow Solid Liquid Gas Keeps Shape Takes Shape of Container Takes Shape of Container Keeps Volume Keeps Volume Takes Volume of Container No No Yes No Yes Yes 6

7 Classify Each of the following as Physical or Chemical Changes Iron metal is melted. Iron combines with oxygen to form rust. Sugar ferments to form ethyl alcohol. 7

8 Classify Each of the following as Physical or Chemical Changes Iron is melted. Physical change describes a state change, but the material is still iron Iron combines with oxygen to form rust.. Chemical change describes how iron and oxygen react to make a new substance, rust Sugar ferments to form ethyl alcohol. Chemical change describes how sugar forms a new substance (ethyl alcohol) 8

9 Elements and Compounds Elements: Substances which can not be broken down into simpler substances by chemical reactions Compounds: Substances that are chemical combinations of elements. Compounds can be broken down into elements: Properties of the compound not related to the properties of the elements that compose it Same chemical composition at all times 9

10 Classification of Matter Matter Pure Substance Constant Composition Homogeneous Mixture Variable Composition Homogeneous = uniform throughout, appears to be one thing pure substances solutions (homogeneous mixtures) Heterogeneous = non-uniform, contains regions with different properties than other regions 10

11 Pure Substances vs. Mixtures Pure Substances Have the same physical and chemical properties Mixtures Have the same composition Homogeneous Separate into components based on chemical properties Different samples may show different properties Variable composition Homogeneous or Heterogeneous Separate into components based on physical properties All mixtures are made of pure substances 11

12 Identify the following as a pure substance, homogeneous mixture or heterogeneous mixture Gasoline A stream with gravel on the bottom Copper metal 12

13 Identify the following as a pure substance, homogeneous mixture or heterogeneous mixture Gasoline a homogenous mixture A stream with gravel on the bottom a heterogeneous mixture Copper metal A pure substance (all elements are pure substances) 13

14 Separation of Mixtures One can separate mixtures based on different physical properties of the components Different Physical Property Boiling Point State of Matter (solid/liquid/gas) Adherence to a Surface Volatility Technique Distillation Filtration Chromatography Evaporation 14

15 Energy and Energy Changes Capacity to do work chemical, mechanical, thermal, electrical, radiant, sound, nuclear Energy may affect matter e.g. raise its temperature, eventually causing a state change All physical changes and chemical changes involve energy changes 15

16 Heat Heat: a flow of energy due to a temperature difference 1. Exothermic = Process results in the evolution of heat. Example: when a match is struck, it is an exothermic process because energy is produced as heat. 2. Endothermic = A process that absorbs energy. Example: melting ice to form liquid water is an endothermic process. 16

17 Units of Energy One calorie is the amount of energy needed to raise the temperature of one gram of water by 1 C kcal = energy needed to raise the temperature of 1000 g of water 1 C joule J = 1 cal 17

18 Example - Converting Calories to Joules Convert 60.1 cal to joules 1cal = joules J 60.1cal = 251J 1cal 18

19 Energy and the Temperature of Matter The increase in the temperature of an object depends on: the amount of heat added (Q) the object s mass 19

20 Specific Heat Specific heat is the amount of energy required to raise the temperature of 1 gram of a substance by 1 Celsius degree By definition, the specific heat of water is g J C Amount of Heat = Specific Heat x Mass x Temperature Change Q = s x m x ΔT 20

21 Example Calculate the amount of heat energy (in joules) needed to raise temperature of 7.40 g of water from 29.0 C to 46.0 C Specific Heat of Water = Mass = 7.40 g J g- C C Temperature Change = 46.0 C 29.0 C = 17.0 C Q = s x m x ΔT J Heat = g 17.0 C = g C 526 J 21

22 Example A 1.6 g sample of metal appears to be gold and requires 5.8 J to raise the temperature from 23 C to 41 C. Is the metal pure gold? ΔT Q = s m ΔT Q s = m ΔT = 41 C - 23 C = 18 C 5.8 J s = 1.6 g x 18 C J = 0.20 g C Table 3.2 lists the specific heat of gold as 0.13 Therefore the metal cannot be pure gold. J g C 22