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3 years ago

What is the definition of physical and chemical changes?

2 answers:

6 0

Physical change, a change that occurs physically, and can also be seen physically. But chemically, it's a change that occurs within the chemical, and most likely not be seen within the eyes, but, has a different charater afterward.

BaLLatris [955]3 years ago

3 0

A physical change in a substance doesn't change what the substance is. In a chemical change where there is a chemical reaction, a new substance is formed and energy is either given off or absorbed. For example, if a piece of paper is cut up into small pieces it still is paper.

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The body uses atoms in different ways to accomplish different tasks. For example, one portion of the body's calcium supply stren

Nikolay [14]

Answer:

The correct option is;

c. the bone contains calcium salts, which are less reactive than the calcium ions found in the blood.

Explanation:

The most abundant metallic element found in the human body is calcium as it is present in the bones teeth and metabolism of the kidney

99 % of the calcium in the human body are found in the bones while the remaining 1 % circulates in the blood as ions

The bones of the vertebrate are made up of calcium salts such as calcium carbonate, calcium phosphate and calcium fluoride.

3 0

3 years ago

How many protons and neutrons in the atom K-42

katovenus [111]

There are 20n nutrons in the atom k-42.

3 0

3 years ago

An alloy with an average grain diameter of 35 μm has a yield strength of 163 Mpa, and when it undergoes strain hardening, the gr

Lera25 [3.4K]

Answer:

$\sigma_y\ =210.2\ MPa$

Explanation:

Given that

d= 35 μm ,yield strength = 163 MPa

d= 17 μm ,yield strength = 192 MPa

As we know that relationship between diameter and yield strength

$\sigma_y=\sigma_o+\dfrac{K}{\sqrt d}$

$\sigma_y\ =Yield\ strength$

d = diameter

K =Constant

$\sigma_o\ =material\ constant$

So now by putting the values

d= 35 μm ,yield strength = 163 MPa

$163=\sigma_o+\dfrac{K}{\sqrt 35}$ ------------1

d= 17 μm ,yield strength = 192 MPa

$192=\sigma_o+\dfrac{K}{\sqrt 17}$ ------------2

From equation 1 and 2

$192-163=\dfrac{K}{\sqrt 17}-\dfrac{K}{\sqrt 35}$

K=394.53

By putting the values of K in equation 1

$163=\sigma_o+\dfrac{394.53}{\sqrt 35}$

$\sigma_o\ =96.31\ MPa$

$\sigma_y=96.31+\dfrac{394.53}{\sqrt d}$

Now when d= 12 μm

$\sigma_y=96.31+\dfrac{394.53}{\sqrt 12}$

$\sigma_y\ =210.2\ MPa$

4 0

3 years ago

My barometer is reading 1253 torr. What is the pressure in mmHg?

kobusy [5.1K]

Answer:

The pressure in mmHg is 1253 (option C)

Explanation:

Two quantities are directly proportional if when multiplying or dividing one of them by a number, the other is multiplied or divided by that number. In other words, the magnitudes are directly proportional when one magnitude increases and so does the other in the same proportion; or when one magnitude decreases and so does the other in the same proportion.

The rule of three or is a way of solving proportionality problems between three known values and an unknown value, which can be applied to directly proportional quantities as follows:

a ⇒ b

c ⇒ x

So $x=\frac{c*b}{a}$

where a, b and c are data and x is the unknown value to be calculated.

In this case, knowing that 1 Torr = 1 mmHg, the rule of three can be applied as follows: if 1 torr is equal to 1 mmHg, 1253 torr is equal to how many mmHg?

$pressure=\frac{1253 torr*1 mmHg}{1 torr}$

pressure= 1253 mmHg

The pressure in mmHg is 1253 (option C)

6 0

3 years ago

Compounds A, B, and C react according to the following equation. 3A(g) + 2B(g) 2C(g) At 100°C a mixture of these gases at equili

Vedmedyk [2.9K]

Answer:

The value of Kc for the reaction is 3.24

Explanation:

A reversible chemical reaction, indicated by a double arrow, occurs in both directions: reagents transforming into products ( direct reaction) and products transforming back into reagents (inverse reaction)

Chemical Equilibrium is the state in which direct and indirect reactions have the same reaction rate. Then taking into account the rate constant of a direct reaction and its inverse the chemical constant Kc is defined.

Being:

aA + bB ⇔ cC + dD

where a, b, c and d are the stoichiometric coefficients, the equilibrium constant with the following equation:

$Kc=\frac{[C]^{c} *[D]^{d} }{[A]^{a} *[B]^{b} }$

Kc is equal to the multiplication of the concentrations of the products raised to their stoichiometric coefficients divided by the multiplication of the concentrations of the reagents also raised to their stoichiometric coefficients.

Then, in the reaction 3A(g) + 2B(g) ⇔ 2C(g), the constant Kc is:

$Kc=\frac{[C]^{2} }{[A]^{3} *[B]^{2} }$

where:

[A]= 0.855 M
[B]= 1.23 M
[C]= 1.75 M

Replacing:

$Kc=\frac{1.75^{2} }{0.855^{3}*1.23^{2} }$

Solving you get:

Kc=3.24

The value of Kc for the reaction is 3.24

8 0

3 years ago