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2 years ago

Why are chemical changes considered “unseen”?

2 answers:

6 0

The correct answer here is that the reason chemical changes can be considered unseen, is because the alterations made within an element when it undergoes a chemical change occurs within the very atoms of the cell itself. In contrast with this, a physical change (such as a solid changing to a liquid through melting) does not change the element itself, but just it's physical form, so this can be seen easily to the human eye.

enot [183]2 years ago

5 0

Answer is: chemical changes are considered "unseen", because they occur at the atomic level.

There are two types of substance changes: chemical and physical.

In chemical change (chemical reaction) new substances are formed, the atoms are rearranged (atoms are invisible to human eyes).

Physical property can be observed and measured without any changes in molecular composition. The same substance is present before and after the psysical change, just with different form or state of matter, this changes are seen by human eyes because of change of color or state of matter.

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A cord is used to vertically lower an initially stationary block of mass m kg at a constant downward acceleration of g/4. the bl

Natali5045456 [20]

(a) We know that work is the product of Force and Distance so: (in this case Distance is negative since going down so –d)

work = force * distance

work = M * (g - g/4) * -d

work = -3Mgd/4 

(b) The work by the weight of the block is simply:

work = Mgd 

(c) The kinetic energy is simply equivalent to the net work, therefore:

KE = net work

KE = Mgd/4 

(d) The velocity is:

v = √(2*KE/M)

Plugging in the value of KE from c:

v = √(2*Mgd / 4M)

v = √(gd / 2)

5 0

2 years ago

A square table has an area of 400 square feet. They want to cut the table into two equal rectangles. If they cut the table in ha

Orlov [11]

Answer:

b=200

l=100

Explanation:

so since it is a square all sides would be equal

when you cut the square vertically the dimensions will change

the bredth would be same that is 200

but the length would be half that is 100

7 0

2 years ago

Suppose you have 81.8 g of Cd. How many Cd atoms are present? Report your answer in scientific notation using the format of 6.02

Lostsunrise [7]

Answer:

1. number of Cd atoms = 4.384 × 10²³

2. number of moles of Ti = 0.817 mol

3. molar mass of C₇H₆O₃ = 138.077 g/mol

4. moles of Sildenafil = 0.249 mmol

Explanation:

1. given data

mass of Cd = 81.8 g

number of Cd atoms = ?

molar mass of Cd = 112.411 g/mol

Solution

1st we find out the number of moles of Cd

number of moles = mass / molar mass

number of moles of Cd = 81.8 g / 112.411 g.mol⁻

number of moles of Cd = 0.728 mol

Now we find out the number of Cd atoms

number of atoms = moles × 6.022 × 10²³

number of Cd atoms = 0.728 (6.022 × 10²³)

number of Cd atoms = 4.384 × 10²³

2. Given data

Mass of Ti = 39.1 g

moles = ?

molar mass Ti = 47.867 g/mol

Solution

Now we will find out the number of moles

number of moles = mass / molar mass

number of moles of Ti = 39.1 g / 47.867 g.mol⁻

number of moles of Ti = 0.817 mol

3. Given data

chemical formula of Salicylic acid = C₇H₆O₃

molar mass of salicylic acid = ?

molar mass of carbon = 12.011

molar mass of hydrogen = 1.008

molar mass of oxygen = 15.999

molar mass of molecule = number of moles of atoms × molar mass of atoms

molar mass of C₇H₆O₃ = 7 (12.011) + 6 (1) + 3 (16)

molar mass of C₇H₆O₃ = 84.077 g + 6 g + 48 g

molar mass of C₇H₆O₃ = 138.077 g/mol

4. Given data

molar mass of Sildenafil = 474.5828 g/mol

mass given = 0.118 g

moles of Sildenafil = ?

Solution

Now we find out the number of moles

number of moles = mass / molar mass

number of moles Sildenafil = 0.118 g / 474.5828 g/mol

number of moles Sildenafil = 0.0003 mol

as this is very small amount we convert it into millimoles

millimoles = moles × 1000

millimoles of Sildenafil = 0.000249 × 1000

millimoles of Sildenafil = 0.249 mmol

4 0

2 years ago

1. Which of the following would likely form a heterogeneous mixture? (Points : 3)

Nata [24]

For the answer to the question above asking which of the following would likely form a heterogeneous mixture?

The answer would be sand and water
other choices like
,baking soda salt and sugar are soluble in water and form homogeneous solution

6 0

3 years ago

Read 2 more answers

Which of the following Group 17 elements is the least reactive?

satela [25.4K]

The given question is incomplete. The complete question is :

Which of the following Group 17 elements is the least reactive

a) Flourine

b) Chlorine

c) Astatine

d) Iodine

Answer: c) Astatine

Explanation:

Halogen is the name given to Group 17 family with general electronic configuration of $ns^2np^5$ which have 7 valence electrons and thus easily gain one electron to attain stable configuration.

As we move down the group from flourine to chlorine to bromine to iodine to astatine , the valence shell moves farther from nucleus and thus tendency to accept the electron decreases and thus reactivity also decreases.

Thus Astatine is the least reactive of all.

7 0

2 years ago