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kirza4 [7]
3 years ago
12

When determining whether a chemical reaction has taken place you observe and look for several indicators. Which would be conside

red an indication that a chemical reaction or chemical change has taken place? es -) A) Solid melts. B) Heat is given off. Substance dissolves D) Substance changes shape. Physical Science​
Chemistry
1 answer:
Phoenix [80]3 years ago
4 0

Answer:

B) Heat is given off.

Explanation:

When heat is given off, a chemical change must have occurred and such a reaction is termed an exothermic reaction.

A chemical change is one in which;

  • the process is not easily reversible
  • leads to the production of new kinds of matter
  • involves change in mass
  • requires a considerable amount of energy.

Most chemical reactions are accompanied by heat changes.

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3 0
2 years ago
6. The graph below shows the heating curve for ethanol (from –200C to 150C). Calculate the amount of heat (kJ) required for each
Kazeer [188]

This problem is providing the heating curve of ethanol showing relevant data such as the initial and final temperature, melting and boiling points, enthalpies of fusion and vaporization and specific heat of solid, liquid and gaseous ethanol, so that the overall heat is required and found to be 1.758 kJ according to:

<h3>Heating curves:</h3>

In chemistry, we widely use heating curves in order to figure out the required heat to take a substance from a temperature to another. This process may involve sensible heat and latent heat, when increasing or decreasing the temperature and changing the phase, respectively.

Thus, since ethanol starts off solid and end up being a vapor, we will find five types of heat, three of them related to the heating-up of ethanol, firstly solid, next liquid and then vapor, and the other two to its fusion and vaporization as shown below:

Q_T=Q_1+Q_2+Q_3+Q_4+Q_5

Hence, we begin by calculating each heat as follows, considering 1 g of ethanol is equivalent to 0.0217 mol:

Q_1=0.0217mol*111.5\frac{J}{mol*\°C}[(-114.1\°C)-(-200\°C)] *\frac{1kJ}{1000J} =0.208kJ\\&#10;\\&#10;Q_2=0.0217mol*4.9\frac{kJ}{mol} =0.106kJ\\&#10;\\&#10;Q_3=0.0217mol*112.4\frac{J}{mol*\°C}[(78.4\°C)-(-114.1\°C)] *\frac{1kJ}{1000J} =0.470kJ\\&#10;\\&#10;Q_4=0.0217mol*38.6\frac{kJ}{mol} =0.838kJ\\&#10;\\&#10;Q_5=0.0217mol*87.5\frac{J}{mol*\°C}[(150\°C)-(78.4\°C)] *\frac{1kJ}{1000J} =0.136kJ

Finally, we add them up to get the result:

Q_T=0.208kJ+0.106kJ+0.470kJ+0.838kJ+0.136kJ\\&#10;\\&#10;Q_T=1.758kJ

Learn more about heating curves: brainly.com/question/10481356

7 0
2 years ago
What is the unit for intensity
Solnce55 [7]

Answer:

Watt or W/m^2

because it is i guess ;--;

6 0
3 years ago
What do physical changes do?
Cloud [144]

Answer:d

Explanation: I just took the test

3 0
3 years ago
Read 2 more answers
Apt A piece of chalk becomes shorter as it is used. Which of the following is NOT true of the shorter piece of chalk?
Tanzania [10]
A. It’s mass has changed if not that’s then it’s B.
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3 years ago
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