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muminat
2 years ago
8

A student is trying to develop a model of an instant heat pack. What is the essential characteristic of the chemical reaction th

at the student should
use to develop the heat pack?
O A The standard enthalpy of reaction should be zero.
о В.
The standard enthalpy of reaction should be negative.
OC. The enthalpy of formation of reactants should be positive.
D. The enthalpy of formation of products should be negative.
Chemistry
1 answer:
Lana71 [14]2 years ago
3 0

The standard enthalpy of reaction should be negative.

<h3>What is enthalpy?</h3>

A thermodynamic quantity equivalent to the total heat content of a system. It is equal to the internal energy of the system plus the product of pressure and volume.

Inside the heat pack are two chemicals that get mixed when you smush them together. As they mix, some weak bonds are broken, which takes a little bit of energy. But new, stronger bonds form which release energy. Releasing that energy causes the surroundings to heat up.

Hence, option B is correct.

Learn more about enthalpy here:

brainly.com/question/13775366

#SPJ1

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A piece of an unknown substance weighing 124.0 grams is heated in boiling water to 100.0oc. when the substance is placed in a ca
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The heat cause 300g water temperature increase from 20 to 26 celcius. The heat transferred would be: 300g * (26 °C -20 °C) *4.2 joule/gram °C= 7560J

The unknown substance is added to the water, so its final temperature should be the same as the water. The calculation would be:

7560J= 124g * (100-26)* specific heat

specific heat= 7560J / 124g / 74 °C= 0.8238 J/gram °C

3 0
3 years ago
What is the ionic charge for the calcium ion in CaCO3?
Lunna [17]
<span>The ionic charge of Calcium (Ca) in calcium carbonate (CaCO3) is 2+. CaCO3 has a neutral ionic charge sin CO3 has a 2- charge.</span>
3 0
3 years ago
Surface tension of solid,liquid and gas​
Arisa [49]

Explanation:

<h3>Surface tension is the tendency of liquid surfaces to shrink into the minimum surface area possible. Surface tension allows insects, usually denser than water, to float and slide on a water surface.</h3>

4 0
3 years ago
Question 20 (3 points) Why is the moon visible? Question 20 options: It is on fire. It reflects sunlight. Earth lights it up. It
alexgriva [62]

20. Answer is "it reflects sunlight".<span>

<span>The moon is </span>not a star<span> <span>as sun. Hence, </span></span>moon can't produce light by itself<span>. The only reason that we can see the moon is </span>it reflects the sunlight<span>. According to the distance from the sun to the moon, the light reflection can be varied.</span>

21. Answer is "Jupiter".

Asteroid belt<span> <span>is a </span></span>region which is located between Mars and Jupiter and consists of asteroids and minor planets.<span> This asteroid belt has the </span>4%<span> <span>as the mass </span>of our moon. Due to the </span>Jupiter's strong gravity<span>, it is </span>prevented a forming of new planet by this asteroid belt.

22.<span> Answer is "</span>they are equal".

The period of revolution is the time which is taken by a mass to go completely one round around another mass. For moon, the period of revolution is 27 days.<span>
The period of rotation</span> is the time taken by a mass to complete one round around its own axis. It is about 27 days for moon. 

</span>23.<span> Answer is "</span>The moon is in Earth's shadow".

<span>Lunar eclipse happens when </span>Sun, Earth and moon are directly aligned each other <span>and Earth is located in between the Sun and the moon. </span>Then the moon is covered by the Earth's shadow.

24.<span> Answer is "</span>In a solar eclipse, it is Earth that is caught in the umbra of the moon. In a lunar eclipse, it is the moon that is caught in the umbra of Earth".

In total lunar eclipse, Earth is located between Sun and the moon and they are directly aligned to each other. The moon is totally covered with the Earth's shadow.
Total solar eclipse can be seen when the moon is located between sun and Earth by completely covering the sun. 

25. According to the given choices, we can get "Apollo"<span> as the answer.

Apollo 8 is the first manned mission to the moon. From that there were several manned mission including <span>first manned landing on the moon. The Apollo program was conducted by USA.</span> </span>

5 0
3 years ago
Which of the compounds below is not an example of a molecular solid?
Goshia [24]
E
Water is the only polar compound so I guess that must be odd one out. I’m sorry I’m of no actual help.
8 0
3 years ago
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