What's the final volume of a gas with an initial volume of 75ml if the pressure decreases from 300ml to 200ml?
2 answers:
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Explanation:
The given data is as follows.
Heat of vaporization () = 45.4 kJ/mol
Specific heat () = 0.903
Let us assume the alcohol given is and its mass is 1.12 g. Also, mass of aluminium block is 73.0 g.
First, calculate the moles of alcohol () as follows.
No. of moles alcohol =
=
= 0.0186 mol
So, heat absorbed by the alcohol () = heat lost by aluminium (
)
=
12.71 =
Thus, we can conclude that the final temperature of the block is 12.3^{o}C[/tex].
Answer : Formation of yellow precipitate is the physical evidence that there has been a chemical reaction.
Explanation :
A chemical reaction happens when 2 or more substances chemically react with each other.
There are 4 evidences indicating that a chemical reaction has occurred which are mentioned below.
1. Change in color : On mixing, the reaction mixture can change color indicating that a chemical change may have occurred.
2. Formation of precipitate : A reaction in which a solid is formed on mixing 2 aqueous solutions is called as precipitation reaction. Here, the formation of solid indicates a chemical change.
ex.
In above reaction, on mixing the solutions, a white precipitate of AgCl is formed which indicates a chemical change.
3. Evolution of gas : A chemical change also occurs when a gas is evolved on mixing 2 substances.
ex.
In above reaction, CO2 gas is evolved and bubbles can be seen in the form of effervescence.
4. Change in temperature : Certain chemical reactions absorb or evolve heat. When a chemical reaction evolves heat, the temperature of the final reaction mixture increases and when it absorbs heat, the temperature decreases. This increase and decrease in temperature indicates a chemical change.
ex.
In above reaction, the final mixture becomes hot as the reaction releases heat. ( Exothermic)
Change in odor also indicates a chemical change.
For the given reaction, a yellow precipitate of PbI2 is getting formed.
Therefore formation of this precipitate is the physical evidence that there has been a chemical reaction.