6. Chemical Reactions (Part 3) (3/5) (Cambridge IGCSE Chemistry 0620 for 2026, 2027 & 2028) — Transcript

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1. 0:00hi everyone welcome to igcc study bu
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8. 0:24learn part three of topic six chemical
9. 0:28reactions
10. 0:30first up reversible reactions and
11. 0:34equilibrium in some reactions the
12. 0:37reactants are completely converted to
13. 0:39products and then the reaction is just
14. 0:43over these are called irreversible
15. 0:47reactions on the other hand some
16. 0:50reactions can go backward meaning the
17. 0:53products can turn back into the original
18. 0:56reactants these are reversible reactions
19. 1:02a reversible reaction is one where the
20. 1:05products of the reaction can react with
21. 1:08each other to form the original
22. 1:12reactants in a reversible reaction the
23. 1:15reaction can proceed in both directions
24. 1:18and this is shown by this
25. 1:22symbol so if a chemical reaction has
26. 1:25this symbol instead of the normal Arrow
27. 1:28then we know it's a reversible reaction
28. 1:31and it can go forward or
29. 1:34backward what is
30. 1:37equilibrium equilibrium refers to a
31. 1:40state where the forward and reverse
32. 1:42reactions in a reversible reaction occur
33. 1:46at the same rate in simpler terms it's
34. 1:49like a balance point where the
35. 1:51concentrations of reactants and products
36. 1:55remain constant over time
37. 2:00so a reversible reaction in a closed
38. 2:03system is at equilibrium when the rate
39. 2:07of the forward reaction is equal to the
40. 2:10rate of the reverse reaction and the
41. 2:14concentration of reactants and products
42. 2:17are no longer
43. 2:21changing let's explore the effects of
44. 2:24changing conditions on reversible
45. 2:28reactions what are hydrated compounds
46. 2:32hydrated compounds are substances that
47. 2:35have water molecules trapped within
48. 2:38their
49. 2:39structure what are anhydrous compounds
50. 2:43anhydrous compounds are substances that
51. 2:46do not contain water molecules within
52. 2:49their
53. 2:52structure both copper 2 sulfate and
54. 2:55Cobalt 2 chloride can exist in both
55. 2:58hydrated and and anhydrous forms that
56. 3:02means they can have water molecules in
57. 3:05them making them hydrated or they can be
58. 3:09without water which makes them
59. 3:14anhydrous first let's take a look at the
60. 3:17effect of heat on hydrated
61. 3:21compounds heating hydrated compounds
62. 3:24makes them lose their water molecules
63. 3:27and become anhydrous
64. 3:32hydrated copper two sulfate is a blue
65. 3:35crystal salt when heat is added to it it
66. 3:39loses its water molecules and becomes
67. 3:42anhydrous it changes color from Blue to
68. 3:51White now let's describe how the
69. 3:54addition of water to anhydrous compounds
70. 3:57can change the direction of a reversible
71. 4:02reaction adding water to anhydrous
72. 4:05compounds can cause them to regain their
73. 4:08water molecules and revert to their
74. 4:11hydrated
75. 4:13form the above change is reversible so
76. 4:17when the water is added to anhydrous
77. 4:19copper to sulfate it can revert back to
78. 4:22its blue hydrated
79. 4:27form Cobalt to two chloride is another
80. 4:31example of a salt that can clearly show
81. 4:34a color change when switching between
82. 4:37its hydrated and anhydrous forms Cobalt
83. 4:412 chloride is a salt that is pink in its
84. 4:45hydrated form heating it makes it lose
85. 4:48its water molecules and it becomes
86. 4:51anhydrous changing color from pink to
87. 4:57blue when water is is added to anhydrous
88. 5:01Cobalt to Chloride it can revert back to
89. 5:04its pink hydrated
90. 5:08form the equilibrium position shows how
91. 5:12much of each substance is present when a
92. 5:15reaction is
93. 5:17balanced for a reversible reaction the
94. 5:21position of equilibrium changes due to
95. 5:24some adjusting
96. 5:27factors this means the balance between
97. 5:30reactants and products
98. 5:35changes these factors affect the
99. 5:37position of
100. 5:39equilibrium changing
101. 5:42temperature changing pressure and
102. 5:46changing
103. 5:49concentration when a reversible reaction
104. 5:52is at equilibrium and then these
105. 5:55external factors are introduced the
106. 5:58reaction system will will respond by
107. 6:01trying to do the opposite to counteract
108. 6:03the change and keep everything
109. 6:06balanced that is restore
110. 6:11equilibrium If It Moves right more
111. 6:14products are made and reactants
112. 6:19decrease If It Moves left more reactants
113. 6:23are present and products
114. 6:27decrease changing temperature in a
115. 6:31reversible reaction One reaction
116. 6:33releases heat that is exothermic while
117. 6:37the other absorbs heat that is
118. 6:40endothermic raising the temperature
119. 6:43shifts the equilibrium toward the
120. 6:46endothermic reaction to absorb heat
121. 6:49while lowering the temperature shifts it
122. 6:52towards the exothermic reaction to
123. 6:54release heat remember these happen to
124. 6:59oppose the
125. 7:02change if the forward reaction is
126. 7:06endothermic raising the temperature will
127. 7:09cause the system to favor the forward
128. 7:12endothermic reaction to absorb the
129. 7:15excess heat thereby Shifting the
130. 7:18equilibrium towards the endothermic
131. 7:22reaction similarly if the forward
132. 7:25reaction is endothermic lowering the
133. 7:28temperature will make the system favor
134. 7:31the backward exothermic reaction to
135. 7:34release more heat Shifting the
136. 7:37equilibrium towards the exothermic
137. 7:42reaction changing pressure this Factor
138. 7:46applies only in reactions with gases we
139. 7:49have to look at the number of moles in
140. 7:52the
141. 7:53reaction increasing the pressure causes
142. 7:56the equilibrium position to shift
143. 7:59towards the side that has fewer gas
144. 8:03molecules this is because the system is
145. 8:05trying to reduce the pressure by
146. 8:08preferring the reaction that produces
147. 8:11fewer gas particles in order to
148. 8:14counteract the pressure increase
149. 8:16remember fewer particles mean lower
150. 8:19pressure let's consider the reaction of
151. 8:22carbon monoxide and hydrogen gas to
152. 8:26produce methane gas and water vapor in
153. 8:29this reaction on the reactant side we
154. 8:33have 1 mole of carbon monoxide gas and 3
155. 8:37mes of hydrogen gas totaling four moles
156. 8:41of gas on the product side we have 1
157. 8:45mole of methane gas and 1 mole of H2O
158. 8:50gas totaling 2 mol of
159. 8:54gas now let's consider the effect of
160. 8:58increasing the pressure
161. 9:00there are more gas molecules on the
162. 9:03reactant side than the product side so
163. 9:07the equilibrium Position will shift to
164. 9:10the right towards the side with fewer
165. 9:13gas molecules the produ side in order to
166. 9:16reduce the
167. 9:18pressure alternatively if the pressure
168. 9:21is decreased the equilibrium Position
169. 9:24will shift towards the side with more
170. 9:27gas molecules which is the reactant side
171. 9:30towards the left this shift occurs to
172. 9:34increase the pressure by favoring the
173. 9:37reaction that involves more gas
174. 9:42molecules changing the pressure only
175. 9:46matters if there are different number of
176. 9:48gas molecules on each side of the
177. 9:52reaction if both sides have the same
178. 9:54number of gas molecules pressure changes
179. 9:58won't affect the equilibrium
180. 10:02position changing the concentration of
181. 10:05reactants will move the equilibrium
182. 10:08position to do the opposite of the
183. 10:12change when we increase the
184. 10:14concentration of reactants the
185. 10:17equilibrium position shifts towards the
186. 10:19products in order to balance it
187. 10:22resulting in an increase in the amount
188. 10:25of products formed
189. 10:29likewise if we reduce the concentration
190. 10:32of reactants the equilibrium shifts
191. 10:35towards the reactants resulting in a
192. 10:38decrease in the amount of products
193. 10:41formed if there's too much of a product
194. 10:44the reaction decreases its amount to
195. 10:47balance the reaction conversely if
196. 10:50there's not enough product the reaction
197. 10:53produces
198. 10:56more very important using a catalyst
199. 11:00will not affect the position of
200. 11:04equilibrium this means that adding a
201. 11:06catalyst won't make the reaction produce
202. 11:09more products or more reactants when it
203. 11:12reaches its balance point but they speed
204. 11:17up reactions they only increase the rate
205. 11:21of reaction they help the reaction reach
206. 11:24equilibrium Faster by increasing the
207. 11:28rate of both the forward and reverse
208. 11:34reactions that concludes part three of
209. 11:38topic six chemical
210. 11:40reactions are you enjoying our videos
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