Answer: The heat needed to be removed to freeze 45.0 g of water at 0.0 °C is 15.01 KJ.
Explanation:
- Firstly, we need to define the term <em>"latent heat"</em> which is the amount of energy required "absorbed or removed" to change the phase "physical state; solid, liquid and vapor" without changing the temperature.
- Types of latent heat: depends on the phases that the change occur between them;
- Liquid → vapor, <em>latent heat of vaporization</em> and energy is absorbed.
- Vapor → liquid, latent heat of liquification and the energy is removed.
- Liquid → solid, <em>latent heat of solidification</em> and the energy is removed.
- Solid → liquid, <em>latent heat of fusion</em> and the energy is absorbed.
- In our problem, we deals with latent heat of freezing "solidification" of water.
- The latent heat of freezing of water, ΔHf, = 333.55 J/g; which means that the energy required to be removed to convert 1.0 g of water from liquid to solid "freezing" is 333.55 g at 0.0 °C.
- Then the amount of energy needed to be removed to freeze 45.0 g of water at 0.0 °C is (ΔHf x no. of grams of water) = (333.55 J/g)(45.0 g) = 15009.75 J = 15.01 KJ.
The scientific models are used because they allow scientists to make predictions and make it easier for scientists to avoid using data. option A and C is correct.
<h3>What are scientific models?</h3>
The scientific models are those which is given by scientists to allow them to make prediction about anything particular on which they are working or making research for it some examples are plum pudding model for an atom and bohr's model of an atom etc.
The biggest advantage is that scientists do not have to check the given data which are written into books they can perform their experiment and can conclude the data by performing experiment.
Therefore, scientific models are used because they allow scientists to make predictions and make it easier for scientists to avoid using data. option A and C is correct.
Learn more about scientific models, here:
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The valence of lead is 4.
Hence the name of the compound is called Lead (IV) oxide.
<h3>Further explanation</h3>
Given
PbO₂ compound
Required
The valence of Pb
Solution
The oxidation number of element O in the compound = -2, except for OF₂ the oxidation state = + 2 and the peroxides (Na₂O₂, BaO₂) the oxidation state = -1 and superoxide, for example KO₂ = -1/2.
The oxidation state in the uncharged compound = 0,
So The oxidation state of Pb :
Pb + 2.(-2) = 0
Pb - 4 = 0
Pb = +4
Answer:
Water has polar O-H bonds. The negative O atoms attract the positive H atoms in nearby molecules, leading to the unusually strong type of dipole-dipole force called a hydrogen bond. Since water has hydrogen bonds, it also has dipole-induced dipole and London dispersion forces.
Hope it helped!!
