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3 years ago

Which definition is correct?

Chemistry

2 answers:

swat323 years ago

8 0

Answer: Option (d) is the correct answer.

Explanation:

A physical change is defined as a change which does not cause any change in chemical composition of a substance.

For example, change in shape, size, mass, volume etc are all characteristics of physical change.

Whereas a change that causes change in chemical composition of a substance is known as chemical change.

For example, $KCl + NaOH \rightarrow NaCl + KOH$

A new substance is always formed in a chemical change.

Thus, we can conclude that the definition a chemical change produces a new substance by breaking and forming new bonds, is correct.

Galina-37 [17]3 years ago

5 0

A physical change can happen without changing any of the characteristics, for example if you have an ice cube which is frozen H2O and you let it sit it will melt only changing the physical appearance and the molecules in the substance. A physical change doesn't change the physical composition.

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aivan3 [116]

Answer:

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Explanation:

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3 years ago

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Acetic acid (HC2H3O2, Ka=1.8x10^-5) is a weak acid. Calculate the pH of an aqueous solution of .25M acetic acid.

tensa zangetsu [6.8K]

Answer: The pH of an aqueous solution of .25M acetic acid is 2.7

Explanation:

$HC_2H_3O_2\rightarrow H^+C_2H_3O_2^-$

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$c-c\alpha$ $c\alpha$ $c\alpha$

So dissociation constant will be:

$K_a=\frac{(c\alpha)^{2}}{c-c\alpha}$

Give c= 0.25 M and $\alpha$ = ?

$K_a=1.8\times 10^{-5}$

Putting in the values we get:

$1.8\times 10^{-5}=\frac{(0.25\times \alpha)^2}{(0.25-0.25\times \alpha)}$

$(\alpha)=0.0084$

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$[H^+]=0.25\times 0.0084=0.0021$

Also $pH=-log[H^+]$

$pH=-log[0.0021]=2.7$

Thus pH is 2.7

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3 years ago

Explain what happens in a nuclear chain reaction

Vesnalui [34]

Answer:

Nuclear Chain Reactions. A chain reaction refers to a process in which neutrons released in fission produce an additional fission in at least one further nucleus. This nucleus in turn produces neutrons, and the process repeats. The process may be controlled (nuclear power) or uncontrolled (nuclear weapons).

Explanation:

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4 years ago

Which group of extremophiles does thermus aquaticus belong to

Elan Coil [88]

Answer:

The correct answer is thermophiles.

Explanation:

Thermus aquaticus are heat resistant bacteria because these bacteria can survive under adverse environmental conditions like high temperature.

These bacteria belong to one of the most heat-loving groups of extremophiles that are thermophiles. Thermophiles are present in volcanic soil, geysers and around deep-sea vents where the temperature is extremely high.

Thermus aquaticus bacteria is used to manufacture an enzyme called Taq DNA polymerase, which is heat resistant and also an important factor in molecular biology.

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4 years ago

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Suggest a method for measuring the size of the colony.

Evgen [1.6K]

Answer:

Counting the number of colonies that arise on a pour plate can calculate the concentration by multiplying the count by the volume spread on the pour plate. Direct counting methods are easy to perform and do not require highly specialized equipment, but are often slower than other methods

Explanation:

I hope it will help you

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3 years ago