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Vilka [71]
3 years ago
10

During chemistry, Dan mixes two clear, colorless solution and mixing them produces a yellow precipitate in a clear, colorless fi

nal solution as shown by the chemical equation.
Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) + 2KNO3(aq)

What physical evidence indicates that there has been a chemical reaction?
Chemistry
1 answer:
kondor19780726 [428]3 years ago
8 0

Answer : Formation of yellow precipitate is the physical evidence that there has been a chemical reaction.

Explanation :

A chemical reaction happens when 2 or more substances chemically react with each other.

There are 4 evidences indicating that a chemical reaction has occurred which are mentioned below.

1. Change in color : On mixing, the reaction mixture can change color indicating that a chemical change may have occurred.

2. Formation of precipitate : A reaction in which a solid is formed on mixing 2 aqueous solutions is called as precipitation reaction. Here, the formation of solid indicates a chemical change.

ex. AgNO_{3} (aq) + NaCl (aq) \rightarrow AgCl (s) + NaNO_{3} (aq)

In above reaction, on mixing the solutions, a white precipitate of AgCl is formed which indicates a chemical change.

3. Evolution of gas : A chemical change also occurs when a gas is evolved on mixing 2 substances.

ex. 2HCl (aq) + Na_{2}CO_{3} (aq) \rightarrow 2NaCl (aq) + H_{2}O (l) + CO_{2} (g)

In above reaction, CO2 gas is evolved and bubbles can be seen in the form of effervescence.

4. Change in temperature : Certain chemical reactions absorb or evolve heat. When a chemical reaction evolves heat, the temperature of the final reaction mixture increases and when it absorbs heat, the temperature decreases. This increase and decrease in temperature indicates a chemical change.

ex.  HCl (aq) + NaOH (aq) \rightarrow NaCl(aq) + H_{2}O (l)

In above reaction, the final mixture becomes hot as the reaction releases heat. ( Exothermic)

Change in odor also indicates a chemical change.

For the given reaction, a yellow precipitate of PbI2 is getting formed.

Therefore formation of this precipitate is the physical evidence that there has been a chemical reaction.

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Why is copper used to make electric wires?​
sesenic [268]

Question:

Copper is used in a variety of applications, one of which is electrical wires. Whether it’s a power cable for a TV, computer, kitchen appliance or construction tool, it’s probably made of copper. Featuring the atomic number 29, this red-brown metal has become essential to our everyday life by helping power countless devices. But copper isn’t the only material that can transmit electricity, so why is it preferred for creating electrical wires?

Answer:

<h2>The two most important factors on why Copper is used to make not just electric wires, but lots of electric related things is that they are Inexpensive and Super Conductive</h2>

Explanation:

Now, I will explain the reasons why these are good things about the copper wire.

<h2>High Conductivity </h2>

Surpassed only by silver, copper is a highly conductive metal. This means electricity can pass through it with greater ease, making it ideal for use in electrical wires. Companies can use other conductive metals to create electrical wires. Unless they use silver, though, the high conductivity properties of copper allow for a greater distance of electrical current travel. Companies can create longer, better performing electrical wires using copper instead of most other conductive metals.

<h2>Inexpensive </h2>

Copper is also relatively inexpensive when compared to other metals. Gold, for example, is an excellent conductor of electricity, but it costs several times more than copper. If companies used gold to manufacture electrical wires, they’d essentially waste money, as copper is more conductive and costs less than its goal counterpart. This alone is reason enough to make copper the de-facto standard for electrical wires.

<h2>High Ductility </h2>

Copper isn’t just conductive; it’s also ductile. In other words, you can bend and flex copper — to some degree — without it breaking or otherwise sustaining damage. Why is this important? Well, electrical wires must often travel through walls, floors, ceilings and other tight spaces. As a result, they’ll naturally bend and snake their way around the home or building in which they are used. The ductile properties of copper allow copper electrical wires to bend and flex. They’ll still transmit electricity, and they won’t lose any power strength from shape deformity.

<h2>Thermal Resistant </h2>

A benefit of copper electrical wires that’s often overlooked is its thermal-resistant properties. According to ESFI, electrical fires are responsible for more than 51,000 residential house fires in the United States each year — and that’s not accounting for commercial/business fires. Copper electrical wires are safer to use than wires made of most other conductive metals because they are resistant to heat.

<h2>As you can see, copper is the preferred metal for electrical wires for several reasons. It has high electrical conductive; it’s inexpensive; it’s ductile; and it’s thermal resistant. This makes is the universally accepted standard for the manufacturing of electrical wires.</h2>

<h2 />
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2 years ago
If you have 3.0 moles of argon gas at STP, how much volume will the argon take up?
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valentinak56 [21]

Answer:

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5 0
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Based on the periodic table why are be, bg, ca and sr in the same column/group/family?
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Answer:

The elements are in the same column/group IIA.

See the explanation below, please.

Explanation:

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