melting

melting and global climate change

Because of global climate change, temperatures all over Earth are rising. However, the melting points of Earths substances, including ice, are constant. The result? Glaciers are melting at an alarming rate. Melting glaciers cause rising sea levels and the risk of dangerous river flooding on land. Click image to the left or use the URL below. URL:

melting point

The temperature at which a substance melts is called its melting point. Melting point is a physical property of matter. The gold pictured in the Figure 1.1, for example, has a melting point of 1064 C. This is a high melting point, and most other metals also have high melting points. The melting point of ice, in comparison, is much lower at 0 C. Many substances have even lower melting points. For example, the melting point of oxygen is -222 C.

from solid to liquid

The process in which rocks or other solids change to liquids is called melting. Melting occurs when particles of a solid absorb enough energy to partly overcome the force of attraction holding them together. This allows them to move out of their fixed positions and slip over one another. Melting, like other changes of state, is a physical change in matter, so it doesnt change the chemical makeup or chemical properties of matter. Q: The molten rock that erupts from a volcano comes from deep underground. How is this related to its liquid state? A: It is always very hot deep underground where molten rock originates. The high temperatures give rock enough energy to melt and remain in a molten state. Underground rock in this state is called magma. Q: What happens to magma after it erupts and starts flowing over the surface of the ground? A: After magma erupts, it is called lava. On the surface, lava eventually cools and hardens to form solid rock. Other substances that are normally solids on Earth can also be heated until they melt. You can see an example in the Figure 1.1. The photo shows molten gold being poured into a mold. When the gold cools, it will harden into a solid gold bar that has the same shape as the mold.

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instructional diagrams

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questions

which of the following statements about melting is true?

a) melting is a chemical change.

-->  b) melting is a change of state.

c) melting changes the chemical properties of matter.

d) some substances do not melt no matter how hot they become.

melted rock below earths surface is known as lava.

a. true

-->  b. false

the melting point of a substance is the same as its freezing point.

-->  a. true

b. false

which of these substances has the lowest melting point?

a) iron

b) gold

c) water

-->  d) oxygen

diagram questions

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