# Changes of State. Heat will change a material from a solid to a liquid to a gas. A liquid evaporates into a gas when it is warmed. It does NOT disappear.

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Changes of State

Heat will change a material from a solid to a liquid to a gas. A liquid evaporates into a gas when it is warmed. It does NOT disappear. A solid melts into a liquid when it is warmed.

Removing heat (cooling) will change a material from a gas to a liquid to a solid. A gas condenses into a liquid when it is cooled. A liquid freezes into a solid when it is cooled Dew is formed when water vapour in the air condenses. On a cold night dew can freeze to form frost.

Changing states Changing the temperature of a substance can result in a change in its state. Below is a diagram showing you how these states are linked together. Melting is when a solid turns into a liquid at its melting point and freezing is the opposite of melting. Boiling is when a liquid is bubbling, the liquid is turning into a gas inside the liquid, at its boiling point. Condensing is a gas turning into a liquid.

of a substance is that temperature when both the solid and the liquid state can exist together. It is the temperature when the solid turns into a liquid or vice versa. The melting point of a substance is that temperature when the gas state of the substance forms bubbles in its liquid. It is boiling! It is the temperature when the liquid turns into a gas. The boiling point is when the solid state of the substance changes into the gas state without going through the liquid state and vice versa. Sublimation

Melting point, boiling point, and density Different substances have different melting points, boiling points and densities. The table shows the melting points, boiling points and densities of a number of substances. Name Symbol or Formula Melting point °C Boiling point °C Density g/cm 3 HeliumHe-270-2690.00017 Carbon (diamond)C355048303.5 NitrogenN2N2 -210-1960.0012 OxygenO2O2 -219-1830.0013 SodiumNa988900.97 ArgonAr-189-1860.0017 IronFe153928877.9 BromineBr-7583.1 TungstenW3377552719.3 MercuryHg-3935713.5 RadonRn-71-620.0089 Sodium ChlorideNaCl80814652.2 Sulphur dioxideSO 2 -75-100.0027 Calcium ChlorideCaCl78216002.5 Carbon dioxideCO 2 -56-780.0018 EthanolC2H6OC2H6O-114780.8 WaterH2OH2O01001.0 Iron oxideFe 2 O 3 145715625.2 Magnesium oxideMgO290036003.6 Name Symbol or Formula Melting point °C Boiling point °C Density g/cm 3 HeliumHe-270-2690.00017 Carbon (diamond)C355048303.5 NitrogenN2N2 -210-1960.0012 OxygenO2O2 -219-1830.0013 SodiumNa988900.97 ArgonAr-189-1860.0017 IronFe153928877.9 BromineBr-7583.1 TungstenW3377552719.3 MercuryHg-3935713.5 RadonRn-71-620.0089 Sodium ChlorideNaCl80814652.2 Sulphur dioxideSO 2 -75-100.0027 Calcium ChlorideCaCl78216002.5 Carbon dioxideCO 2 -56-780.0018 EthanolC2H6OC2H6O-114780.8 WaterH2OH2O01001.0 Iron oxideFe 2 O 3 145715625.2 Magnesium oxideMgO290036003.6 Name Symbol or Formula Melting point °C Boiling point °C Density g/cm 3 HeliumHe-270-2690.00017 Carbon (diamond)C355048303.5 NitrogenN2N2 -210-1960.0012 OxygenO2O2 -219-1830.0013 SodiumNa988900.97 ArgonAr-189-1860.0017 IronFe153928877.9 BromineBr-7583.1 TungstenW3377552719.3 MercuryHg-3935713.5 RadonRn-71-620.0089 Sodium ChlorideNaCl80814652.2 Sulphur dioxideSO 2 -75-100.0027 Calcium ChlorideCaCl78216002.5 Carbon dioxideCO 2 -56-780.0018 EthanolC2H6OC2H6O-114780.8 WaterH2OH2O01001.0 Iron oxideFe 2 O 3 145715625.2 Magnesium oxideMgO290036003.6 ELEMETSELEMETS NameSymbol or Formula Melting point ºC Boiling point ºC Density s/cm 3 Nitrogen N2N2 - 210- 1960,0012 Bromine Br - 7 583,1 Oxygen O2O2 - 219- 1830,0013 Iron Fe 153928877,9 Mercury Hg -3935713,5 COMPOUNDSCOMPOUNDS Water H2OH2O01001,0 Ethanol C2H6OC2H6O-56-780,8 Carbon dioxide CO 2 -56-780,0018 Iron oxide Fe 2 O 3 145715625,2

State of a substance at room temperature Here is a method for working out if a substance is a solid, liquid or gas at room temperature. This question is often asked in your tests. 1.Look up the substance's melting and boiling points 3. Put the melting, boiling point and room temperature (this is always 20°C) on the number line. 2. Draw a number line 4. Label it solid below melting point, liquid between the melting and boiling points and gas above the boiling point. 5. The state of the substance at room temperature is shown when looking at 20°C, room temperature.

Bromine Melting point Room temperature Boiling point Bromine is a liquid at room temperature. Nitrogen Melting pointBoiling point Room temperature Nitrogen is a gas at room temperature. Do the same with the others!

What happens during state change? When a substance melts it changes from a solid to a liquid. During this change the temperature remains constant. The energy supplied causes the bonds between the particles in the solid to break. Similarly, when a liquid is boiling its temperature does not rise. The energy goes to overcome the forces between the particles in the liquid turning the liquid into a gas. A heating curve shows this in more detail.

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