Answers:
1. When the temperature in a room increases from25°C to 33°C, galium changes from a solid to a liquid.
2. In a lab, methane and nitrogen are cooled from -170°C to -200°C. The methane freezes and the nitrogen condenses.
3. When gold is heated to 2,856°C it changes from a liquid to a gas
Explanations:
The melting and boiling point of the substances permit to state whether a susbstance will be solid, liquid or gas at certain conditions (temperature in this case).
Melting point: is the temperature at which a solid becomes liquid.
Boiling point is the temperature at which a liquid becomes gas.
Hence:
- if the temperature is below the melting point, the substance is solid.
- if the temperature is between the melting and the boiling points, the substance is liquid.
- if the emperature is above the boiling point the substance is gas.
The names of the phase changes dealt with in this question are:
- Condenstation: pass from gas to liquid.
- Boiling (Vaporization): pass from liquid to gas
- Freezing: pass from liquid to solid.
- Melting (fusion): pass from solid to liquid
With that let us go through the three statements:
1. When the temperature in a room increases from25°C to 33°C,
______ changes from a solid to a liquid. Answer: galium.
You need to find in the table a substance whose melting point is between 25°C and 33°C.
This is Gallium, whose melting point is indicated to be 30°C, meaning that at 25°C it is solid and at 33°C it is liquid.
2. In a lab, methane and nitrogen are cooled from -170°C to -200°C. The methane freezes and the nitrogen _____. Answer: condenses.
Since the boling point of nitrogen is - 196°C, at -170°C nitrogen is gas.
Since, the melting point is - 210°C, at -200°C, nitrogen is liquid.
So, nitrogen condenses when it is cooled from - 170°C to - 200°C.
3. When gold is heated to 2,856°C it changes from a liquid to a ____. Answer: gas.
Since, 2856°C is the boiling point of gold, it will start fo pass from liquid to gas at this temperature.