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1.why do amphorous solids not have definite melting point and heat of fusion? 2.why is glass considered as super cooled liquid? 3.if molecules are held together by weak dispersion forces,can they exist as crystilline solid? 4.can non crystalline solids be converted to crystalline solid? explain with example. 5.why is graphite soft and good lubricant?

1.why do amphorous solids not have definite melting point and heat of fusion?


2.why is glass considered as super cooled liquid?


3.if molecules are held together by weak dispersion forces,can they exist as crystilline solid?


4.can non crystalline solids be converted to crystalline solid? explain with example.


5.why is graphite soft and good lubricant?


Grade:12

1 Answers

Vasantha Kumari
askIITians Faculty 38 Points
7 years ago

1. Amorphorous solids do not have definite geometrical form and do not possess a specific geometric shape. Their melting point is not definite and they can easily flow without undergoing a sharp change such as changing into a liquid. The characteristic feature of heat of fusion is absent in amorphous solids.

2. Glass is an amorphous solid that doesn’t have a sharp melting point, but melts over a range of temperature. While we heat glass it first softens and then melts over a temperature range. Hence, glass is suitable for moulding and blowing into various shapes.

3. Molecules that are held together by weak dispersion forces cannot exist at crystalline solids since the atoms are arranged in a regular repetitive pattern in a crystalline solid. If the molecules were weakly held by dispersion force, then on heating the solid will soften quickly. Moreover a crystalline structure is the preferred state for most of the solids as it is a low energy state.

4. Non crystalline solids or amorphous solids can be converted to crystalline solids at high temperature. For example silica exists both as crystalline and amorphous forms. Quartz is more commonly used industrial silica and can be converted into amorphous form by extensive heating.

5.Graphite is a hard and brittle due to strong covalent bonds and possess high melting and boiling points. There exists a larger distance between the layers that remain adjacent to each other when compared to the carbon-carbon bond length. Thus, these layers can slip over one another easily and is the reason for graphite being a soft and good lubricant.

Vasantha,

AskIITian Expert,

MSc, B.Ed

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