4th Quarter Review - Chemical Reactions - 7th Grade

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by Leopoldo Busato Munhoz De Castro1 view·Updated Nov 20, 2020
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  1. Hello, seventh graders.
  2. How are you doing today?
  3. Welcome back to our recorded sciences class.
  4. Today we will recap the most important topics from unit
  5. number nine.
  6. Chemical reactions cover during the fourth quarter.
  7. Okay, before we start, it's important to say that chemical
  8. reactions are a sensual to our lives.
  9. They are everywhere, including inside of our body.
  10. Chemical reactions involved in respiration allow living organisms to release
  11. the energy that keep them alive.
  12. So let's start answering the question.
  13. What is a chemical reaction?
  14. Chemical reaction occurs when chemical bonds between the atoms in
  15. the molecule or a compound change some chemicals reactions create
  16. products from simpler chemicals or even its elements.
  17. Other reactions break more complex compound into smaller products.
  18. In other words, a chemical reaction.
  19. Of course, when chemical bones are broken or form it,
  20. this means that reactant and the products are different chemicals.
  21. Here in our presentation, there is how we can describe
  22. them using word equations.
  23. This is the word equation for the chemical reaction called
  24. photosynthesis. Carbon dioxide plus water zika to glucose plus oxygen,
  25. carbon dioxide and water are the reactant ce reactant are
  26. the chemical substances that are used in a reaction, and
  27. glucose and oxygen are the products which are the chemical
  28. substances that are produced it in a reaction reactant.
  29. Our place is always at the left hand side off
  30. the equation and the products always at the right hand
  31. side. Okay, now take a look at another example.
  32. When magnesia in reacts with hydrochloric acid, they produce magnesium
  33. chloride and hydrogen, however, be attention to their atoms in
  34. both sides.
  35. Off equation, there are exactly the same amount and types
  36. of atoms.
  37. After the chemical reactions, the elements off the reactant are
  38. just rearrange it into new combinations in the products.
  39. So to make a long story short during a chemical
  40. reaction, no element which is present in the reactant, disappears
  41. in the products.
  42. And also no new element appears in the products.
  43. The atoms air simply rearranged into new combinations.
  44. No atoms are lost.
  45. No new atoms are produce it right?
  46. So what evidence suggests a chemical reaction has taken place.
  47. A chemical reaction take place on a time scale with
  48. changes in the bonding between atoms.
  49. It is not possible to observe this directly.
  50. However, there are often clues that might suggest that a
  51. chemical reactions taking place, call or change because a change
  52. in color mean that a chemical reaction has formed gas
  53. release. If a gas is released, this might show that
  54. a chemical reaction has taken place in liquids.
  55. Look for bubbles appearing right.
  56. This smells I smell that was not there before.
  57. Might show that a chemical substance has form.
  58. It precipitated forms.
  59. When two liquids are mix it a solid, sometimes forms.
  60. This is called precipitate and temperature change.
  61. Many chemical reactions.
  62. We kind energy or release it.
  63. This caused the temperature to decrease or increase right.
  64. But what causes a chemical reaction?
  65. Chemical reaction, Of course.
  66. When bones between atoms are made or broken, it takes
  67. energy to break bones between atoms.
  68. This is called decomposition, and energy is released it when
  69. bones, air farm and then we call synthesis most.
  70. The composition reactions require heat to be supplied for a
  71. compound to be broken into two or more simpler molecules,
  72. which means that these reactions absorbed energy from the surroundings.
  73. The type of reaction which requires more energy should be
  74. supply it than it releases its called under term IQ.
  75. The opposite, often under thermic reaction, is called an excellent
  76. thermic reaction.
  77. An extra thermic reaction may require some energy to be
  78. supplied to break the existing chemical bones.
  79. In the reactant CE, however, more energy is released by
  80. farming the chemical bonds in product, so these reactions release
  81. his energy into the surroundings.
  82. Right now, let's recap the most important groups off chemical
  83. substance that we have discussed during the last quarter assets
  84. basis for alk allies and salts.
  85. Starting with assets, there is an important class off chemicals
  86. called assets.
  87. You may be familiar with citric acid, which occurs in
  88. foods or ascetic acid, which is present in vinegar.
  89. Assets that are more common in laboratory are so for
  90. ic acid, hydrochloric acid and nitric acid.
  91. Many assets are corrosive substances, which means that eats away
  92. in erodes.
  93. Other materials assets take part in different chemical reactions, and
  94. I present in different products off our daily life.
  95. Some substance can neutralize assets, and I taught off as
  96. the opposite of assets.
  97. These substance are called basis, some basis, dissolves on water
  98. and are called alkali.
  99. The most commonly used alkaline solutions in the laboratory are
  100. sodium hydroxide and ammonium hydroxide.
  101. Strongly alkaline solutions can also be corrosive, and bases and
  102. alkali eyes are also very common.
  103. Different cleaning products contain alkali eyes, for example.
  104. Okay, assets and alkali eyes can be measured on the
  105. B age scale, which runs from 0 to 14.
  106. This is the best way to identify if a substance
  107. is acidic or basic.
  108. From 0 to 6.
  109. The substance is acidic, being zero the strongest exit and
  110. six the weakest.
  111. The midpoint off the scale, a pH of seven, represents
  112. a solution that is neither acidic or alkaline, which means
  113. that the substance is neutral, such as pure water.
  114. From 8 to 14.
  115. The substance is basic or alkaline, being eight the weakest
  116. base and 14.
  117. The strongest right pH can be tested using indicators.
  118. There are many different indicators, but she commonly used indicators
  119. are universal indicator solution and universal indicator.
  120. Paper indicators are chemicals that show us the P age
  121. off different substances.
  122. When an acid reacts with base, the reaction is called
  123. a neutralization reaction.
  124. This type of reaction will produce water, and in order
  125. to distance that it's called salt, assault is formed.
  126. When an acid is neutralize it by a base or
  127. an alkali.
  128. The type off acid will determine the type off salt
  129. that is produce it.
  130. The other part off the salts name comes from the
  131. base or alkali, for example, when sodium hydroxide and alkali
  132. reacts with hydrochloric acid, the reaction produces a salt called
  133. sodium chloride, plus water.
  134. When copper oxide a base reacts with Sufi uric acid,
  135. the reaction produces assault called copper so fit plus water.
  136. Okay, now let's talk a little bit about the reactions
  137. with metals.
  138. Metals can react with the oxygen in the air, and
  139. this reaction forms a metal oxide.
  140. When Eireann reacts with oxygen, it produces, Eireann knocks side.
  141. Some matters react in contact with air and the common
  142. name off.
  143. This reaction is resting, but the scientific name for this
  144. kind of reaction is oxidation.
  145. Okay? Different metals react with oxygen in different ways.
  146. Some metals are highly reactive, others are not reactive at
  147. all. So are called un reactive.
  148. Metals also react with water, and in that case they
  149. formed a metal hydroxide.
  150. Okay, so metals react with oxygen, water and acids in
  151. different ways, so they can be organize it in order
  152. off their reactivity.
  153. The least off metals reactivity is called the reactivity serious,
  154. right? As we go down the reactivity serious list, the
  155. metals become less reactive.
  156. And here in our presentation, we have quotation as the
  157. most reactive metal and Patino as the least reactive.
  158. The reactivity Siri's also determines how metals and compounds that
  159. contain these metals We will react with each other.
  160. A more reactive metal can be used to displace allows
  161. reactive metal for a compound.
  162. Then this reaction is called displacement reaction.
  163. Okay, so, seventh graders this week during our life class,
  164. we will discuss a little bit more about Unit nine
  165. chemical reactions.
  166. Okay, so see you all there.
  167. Thank you very much for your time and bye bye.