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Chapter 4: Changes in matter

Chapter 4: Changes in matter. Changes in matter. Physical change Chemical change Nuclear transformations. Physical changes. Physical changes alter neither the nature nor the characteristic properties of matter. Atoms and molecules of the substance do not change. Examples: _boiling water

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Chapter 4: Changes in matter

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  1. Chapter 4: Changes in matter

  2. Changes in matter • Physical change • Chemical change • Nuclear transformations

  3. Physical changes Physical changes alter neither the nature nor the characteristic properties of matter. Atoms and molecules of the substance do not change. Examples: _boiling water _melting ice _broken tree`s branches

  4. Chemical changes Chemical changes alter the nature and the characteristic properties of matter. The bonds between atoms are rearranged, and new molecules are formed. Examples: _rusting iron _burning tree

  5. Nuclear transformation Nuclear transformations involve the rearrangement of the particles making up the atomic nucleus, with new elements being formed.

  6. Chemical changes Signs that point to the occurrence of a chemical change: • Release of a gas. • Emission or absorption of heat. • Emission of light. • Change in colour. • Formation of a precipitate.

  7. Chemical Equations Chemical changes = Chemical equations A (s) + B (l) C (aq) + D (g) Physical-state symbols: (s): solid (l): liquid (aq): aqueous (g):gas

  8. Law of Conservation of Mass The law of conservation of mass states that the total mass of reactants is always equal to the total mass of products. _This implies that the nature of the atoms involved in the chemical reaction is not altered by the reaction, only the bonds between the atoms. CH4(g) + 2 O2(g) CO2(g) + 2 H2O (g) 16g + 64 g = 80 g 44g + 36g = 80g

  9. Types of chemical reactions • Synthesis: 2 or more reactants combine to form a new product. N2(g) + 2 O2(g) 2 NO2(g) 2) Decomposition: A compound separates into two or more compounds (opposite to synthesis). 2H2O (l) 2 H2(g) + O2(g)

  10. Types of chemical reactions 3) Precipitation: The combination of two solutions with the formation of an insoluble or only slightly soluble substance (a precipitate) is formed. _It is often possible to predict whether combining two solutions will result in the formation of a precipitate. See table 4.16, page 118 textbook for more details. NaCl(aq) + AgNO3(aq) NaNO3(aq) + AgCl(s)

  11. Types of chemical reactions 4) Acid-base neutralization: An acid and a base react producing a Salt and Water. _When the number of H+ ions (acid) equals the number of OH- ions (base), the solution is said to be neutral (pH = 7). HCl(aq) + NaOH(aq) NaCl(aq) + H2O (l)

  12. Types of chemical reactions 5) Oxidation: Chemical change involving oxygen or a substance with properties similar to those of oxygen. _We humans live and die because of oxidation. Through cellular respiration we use oxidation to live. However, through oxidation our cells age. _Oxidation is prompted by the presence of light or humidity. In order to combat oxidation of metals like Iron, a process called galvanization is used. This means coating iron with zinc (a much less oxidizing metal). Similarly, antioxidants and preservatives are added to food to prolong its shelf life. 2 Ca(s) + O2(g) 2 CaO(s)

  13. Types of chemical reactions 6) Combustion: Special form of oxidation that releases a large amount of energy. _Burning wood and cellular respiration are examples of combustion reactions. 2 Fe (s) + O2(g) 2 FeO(s) _Burning fuels is a combustion reaction that ultimately yields carbon dioxide (CO2) and water. That is why the activity of burning fuels at massive scale is said to contribute to the greenhouse effect as it increases the concentration of carbon dioxide in the atmosphere.

  14. Types of chemical reactions Combustion needs the fire triangle: _Fuel (hydrocarbons, fossil fuels, wood, etc). _Oxidizing agent (usually oxygen). _Heat (enough to reach the ignition temperature, that is the minimum value of temperature needed to combust a fuel.

  15. Types of chemical reactions 7) Cellular respiration: Chemical change in which glucose and oxygen are used to generate energy, also producing carbon dioxide and water. C6H12O6(s) + 6O2(g) 6CO2(g) + 6H2O (l) + E

  16. Types of chemical reactions 8) Photosynthesis: Opposite to cellular respiration, therefore endothermic, it implies the use of solar energy to produce glucose and oxygen from carbon dioxide and water. 6CO2(g) + 6H2O (l) + Solar E C6H12O6(s) + 6O2(g) _Organism that carry out photosynthesis form the basis of all food chains. They are referred to as Producers because they use sunlight to produce the organic matter other living organisms need to survive.

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