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vitfil [10]
3 years ago
14

The highly exothermic thermite reaction, in which aluminum reduces iron(iii) oxide to elemental iron, has been used by railroad

repair crews to weld rails together. 2al(s) + fe2o3(s)  2fe(s) + al2o3(s) h = –850 kj what mass of iron is formed when 725 kj of heat are released?
Physics
1 answer:
trapecia [35]3 years ago
6 0

Answer:

To illustrate clearly, I will rewrite the reaction in a more understandable manner.

2 Al(s) +  Fe₂O₃ (s) ⇒ 2 Fe(s) + Al₂O₃(s)                Δhrxn = –850 kJ

This reaction has a negative sign for the change in enthalpy of reaction. The sign convention only means that the reaction releases energy to the surroundings. In other words, the reaction is exothermic. Focusing on only its magnitude, this means that 850 kJ of energy is needed for this reaction of 2 Aluminum moles and 1 mole of Fe₂O₃  to occur. 

Now, if you only had an energy of 725 kJ, then the reaction is incomplete but it will still form Iron (Fe). We use stoichiometric calculations as follows:

725 kJ * (2 mol Fe/850 kJ) = 1.7 moles of Fe

Knowing that the molar mass of Fe is 55.6 g/mol, then the mass of produced iron is

1.7 mol Fe * 55.6 g/mol = 94.85 g iron

Explanation:

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Answer:

160 m

Explanation:

The intensity, I, of the sound is inversely proportional to the square of the distance, r, from the source.

I\propto \dfrac{1}{r^2}

Hence,

I_1r_1^2 = I_2r_2^2

r_2 = r_1\sqrt{\dfrac{I_1}{I_2}}

From the question, I_2 is half of I_1

r_2 = r_1\sqrt{\dfrac{I_1}{0.5I_1}}

r_2 = r_1\sqrt{2}

r_2 = 113\text{ m}\sqrt{2} = 160 \text{ m}

3 0
3 years ago
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Explanation

     it is a force

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3 years ago
Suppose you throw a baseball downward from a roof so that it initially has 120 J of gravitational potential energy, and 10 J of
Volgvan

Answer:

B.

It will be greater than 10 J.

Explanation:

The total mechanical energy of an object is the sum of its potential energy (PE) and its kinetic energy (KE):

E = PE + KE

According to the law of conservation of energy, when there are no frictional forces on an object, its mechanical energy is conserved.

The potential energy PE is the energy due to the position of the object: the highest the object above the ground, the highest its PE.

The kinetic energy KE is the energy due to the motion of the object: the highest its speed, the largest its KE.

Here at the beginning, when it is at the top of the roof, the baseball has:

PE = 120 J

KE = 10 J

So the total energy is

E = 120 + 10 = 130 J

As the ball falls down, its potential energy decreases, since its height decreases; as a result, since the total energy must remain constant, its kinetic energy increases (as its speed increases).

Therefore, when the ball reaches the ground, its kinetic energy must be greater than 10 J.

7 0
3 years ago
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Identify each picture as either an inelastic collision or elastic collision
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Answer:

<u>Inelastic collision:</u>

A collision in which there is a loss of Kinetic Energy due to internal friction of the bodies colliding.

<u>Characteristics of an inelastic collision:</u>

  • <em>the momentum of the system is conserved</em>
  • <em>the momentum of the system is conservedloss of kinetic energy</em><u> </u>

<em>I</em><em>n</em><em> </em><em>a perfectly elastic collision</em><em>, the two bodies </em><em>that</em><em> </em><em>collide with each other stick together.</em>

<u>Elastic </u><u>collision</u><u>:</u>

A collision in which the kinetic energy of the two bodies, before and after the collision, remains the same.

<u>Characteristic</u><u>s</u><u> </u><u>of</u><u> </u><u>elastic</u><u> </u><u>collision</u><u>:</u>

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In everyday life, no collision is perfectly elastic.

__________________

ANSWER:

<u>Given examples:</u>

  • Two cars colliding with each other form an example of inelastic collision.

<u>Reason:</u>

<em>(</em><em>T</em><em>hey</em><em> </em><em>lose</em><em> </em><em>kinetic</em><em> </em><em>energy</em><em> </em><em>and</em><em> </em><em>come</em><em> </em><em>to</em><em> </em><em>a</em><em> </em><em>stop</em><em> </em><em>after</em><em> </em><em>the</em><em> </em><em>collision</em><em>.</em><em>)</em>

  • A ball bouncing after colliding with a surface is an example of elastic collision

<u>Reason:</u>

<em>(a very less amount of kinetic energy is lost)</em>

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Answer:

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8 0
3 years ago
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