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March 29, 2024, 09:13:22 pm

Author Topic: Chemistry Misunderstandings  (Read 2003 times)  Share 

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Sine

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Chemistry Misunderstandings
« on: January 13, 2020, 02:35:12 pm »
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The aim of this thread is to dispel any misunderstandings or mistruths within the subject of chemistry. Hopefully, this will give everyone a better understanding of the subject, allow everyone to revise chemistry concepts and stop students from falling into some of the common traps of understanding.

E.g. A pair of posts in this thread would be in the following form
Post 1: -misunderstanding- (in italics or clearly labelled to reduce confusion)
Post 2: -explain what the truth actually is (at a year 11-12 level)

For example:
User 1: A system is in equilibrium when the forward and backward reactions stop occurring.
User2: A system is in equilibrium when the rate of the forward and backward reactions are equal. Also, the concentrations of the reactants and products are constant.

Everyone is encouraged to participate in this thread whether you have just started studying chemistry this year or have a degree in it  :)

I’ll begin
Misconception: Enzymes catalyze chemical reactions that would never occur in the absence of an enzyme
 

caffinatedloz

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Re: Chemistry Misunderstandings
« Reply #1 on: January 14, 2020, 06:43:11 am »
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Misconception: Enzymes catalyze chemical reactions that would never occur in the absence of an enzyme
Enzymes act as a catalyst, that means that they increase the speed/rate at which specific reactions occur. However, that is not to say that these reactions would not and could not occur without enzymes. These reactions could occur in the absence of an enzyme however that would happen at a slower rate.

Misconception: Elements on the periodic table are all substances found in nature.

Chocolatemilkshake

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Re: Chemistry Misunderstandings
« Reply #2 on: January 14, 2020, 07:49:12 am »
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Misconception: Elements on the periodic table are all substances found in nature.

The majority of elements between 1 to 92 are present in nature (although some only occur in very small amounts). However, most of the other elements (with higher amounts of protons) on the periodic table are not found naturally on earth and can only be artificially produced in a lab.

Fun fact: Technetium (element 42) was the first element to be artificially produced. It is the only element below uranium that does not naturally exist on this earth.

Misconception: In a titration, the end point and the equivalence point are the same thing.
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sk2000

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Re: Chemistry Misunderstandings
« Reply #3 on: January 14, 2020, 08:30:11 am »
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The majority of elements between 1 to 92 are present in nature (although some only occur in very small amounts). However, most of the other elements (with higher amounts of protons) on the periodic table are not found naturally on earth and can only be artificially produced in a lab.

Fun fact: Technetium (element 42) was the first element to be artificially produced. It is the only element below uranium that does not naturally exist on this earth.

Misconception: In a titration, the end point and the equivalence point are the same thing.

The equivalence point is a point during titration when the solutions have been mixed in the exact mole ratio seen in the reaction equation. The end point, on the other hand, occurs just after the equivalence point and is the point during a titration when the indicator changes colour.

The end point is not observed at the equivalence point, rather when the equivalence point is exceeded and there is an imbalance in acid or base.

Misconception: Hydrogen fuel cells do not emit greenhouse gases
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Erutepa

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Re: Chemistry Misunderstandings
« Reply #4 on: January 14, 2020, 11:11:07 am »
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Misconception: Hydrogen fuel cells do not emit greenhouse gases
I must say this is a great misconception that I am sure many fall into the trap of!
Hydrogen fuel cells only produce water (specifically water vapour) through their operation. While many would not at first think water to  be a greenhouse gas (presumably most people go strait to thinking of CO2 when greenhouse gas is mentioned), water vapour is infact a greenhouse gas. This is becuase a greenhouse gas is any gas which 'traps' heat (but absorbing and remitting radiation (specifcally infrared)), something which water vapour does do, hence classifying it as a greenhouse gas!

misconcenption: the equilibrium constant of a reaction is dependent on the pressure of the system
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Othello

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Re: Chemistry Misunderstandings
« Reply #5 on: January 14, 2020, 12:45:16 pm »
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misconcenption: the equilibrium constant of a reaction is dependent on the pressure of the system

The equilibrium constant is only affected by the temperature of the system. Pressure and concentrations do not affect it. Instead, pressure and concentrations affect the equilibrium position of the reaction. The equilibrium constant shows the extent to which the reaction will occur (ie whether it goes to completion in the forward direction), whereas the equilibrium position is the point at which neither the forward nor reverse reaction is spontaneous. Furthermore, for a given reaction and temperature, there can only be one equilibrium constant, but multiple equilibrium positions. 

Misconception:  ALL combustion reactions are exothermic
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Bri MT

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Re: Chemistry Misunderstandings
« Reply #6 on: January 28, 2020, 08:25:52 am »
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The equilibrium constant is only affected by the temperature of the system. Pressure and concentrations do not affect it. Instead, pressure and concentrations affect the equilibrium position of the reaction. The equilibrium constant shows the extent to which the reaction will occur (ie whether it goes to completion in the forward direction), whereas the equilibrium position is the point at which neither the forward nor reverse reaction is spontaneous. Furthermore, for a given reaction and temperature, there can only be one equilibrium constant, but multiple equilibrium positions. 

Misconception:  ALL combustion reactions are exothermic

Mind explaining your misconception? :)

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Re: Chemistry Misunderstandings
« Reply #7 on: January 28, 2020, 09:09:54 am »
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The equilibrium constant is only affected by the temperature of the system. Pressure and concentrations do not affect it. Instead, pressure and concentrations affect the equilibrium position of the reaction. The equilibrium constant shows the extent to which the reaction will occur (ie whether it goes to completion in the forward direction), whereas the equilibrium position is the point at which neither the forward nor reverse reaction is spontaneous. Furthermore, for a given reaction and temperature, there can only be one equilibrium constant, but multiple equilibrium positions. 

Misconception:  ALL combustion reactions are exothermic

Most combustion reactions are exothermic and release energy into the surroundings. However, some reactions such as N2(g)+ O2--> 2NO(g) are endothermic because of the high amount of energy needed to break the nitrogen triple bond and oxygen double bond. This results in the formation of NO, however, the energy released when the products are formed is less than the energy required to break bonds.

Misconception-> Adding an inert gas to the system will alter the position of equilibrium as the pressure of the vessel has increased
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Othello

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Re: Chemistry Misunderstandings
« Reply #8 on: January 28, 2020, 12:06:58 pm »
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Most combustion reactions are exothermic and release energy into the surroundings. However, some reactions such as N2(g)+ O2--> 2NO(g) are endothermic because of the high amount of energy needed to break the nitrogen triple bond and oxygen double bond. This results in the formation of NO, however, the energy released when the products are formed is less than the energy required to break bonds.

Yep, that was the answer I was looking for.
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