Understanding Change of State Graphs: Heating and Cooling
Understanding Change of State Graphs
A change of state graph represents the time and temperature values of a substance as its state changes. Time is the independent variable (x-axis). The x-axis shows time and its units (in parentheses). Temperature is the dependent variable (y-axis). The y-axis shows temperature and its units (in parentheses).
Heating Graphs
In a heating graph (where temperature increases), we can differentiate five sections:
Section 1: Temperature Increase (Solid)
This section is a slanted line (going up), indicating a temperature increase. For example, the temperature increases from -15°C to 5°C. We heat a solid, and it absorbs heat. Its particles vibrate more, but do not move around each other. The forces of attraction between particles are very strong. The state of aggregation is solid.
Section 2: Fusion (Melting)
This section is a horizontal line, indicating constant temperature. This represents a change of state: fusion (or melting), a transition from solid to liquid. The temperature remains constant at the melting point (e.g., T = 5°C). We have two states of aggregation: solid + liquid.
Section 3: Temperature Increase (Liquid)
This section is a slanted line (going up), indicating a temperature increase. For example, the temperature increases from 5°C to 55°C. We heat a liquid, and it absorbs heat. The particles can separate sufficiently from each other. The state of aggregation is liquid.
Section 4: Vaporization (Boiling)
This section is a horizontal line, indicating constant temperature. This represents a change of state: vaporization (boiling), a transition from liquid to gas. The temperature remains constant at the boiling point (e.g., T = 55°C). We have two states of aggregation: liquid + gas.
Section 5: Temperature Increase (Gas)
This section is a slanted line (going up), indicating a temperature increase. We heat a gas, and it absorbs heat. The particles can separate from each other and move around. The forces of attraction between particles are very weak. The state of aggregation is gas.
The melting point and the boiling point are specific properties of matter.
Cooling Graphs
In a cooling graph (where temperature decreases), we can differentiate five sections:
Section 1: Temperature Decrease (Gas)
This section is a slanted line (going down), indicating a temperature decrease. For example, the temperature decreases from 80°C to 60°C. We cool a gas, and it releases heat. The particles can separate from each other and move around. The forces of attraction between particles are very weak. The state of aggregation is gas.
Section 2: Condensation
This section is a horizontal line, indicating constant temperature. This represents a change of state: condensation, a transition from gas to liquid. The temperature remains constant at the condensation point (e.g., T = 60°C). We have two states of aggregation: gas + liquid.
Section 3: Temperature Decrease (Liquid)
This section is a slanted line (going down), indicating a temperature decrease. For example, the temperature decreases from 60°C to 25°C. We cool a liquid, and it releases heat. The particles can separate sufficiently from each other. The state of aggregation is liquid.
Section 4: Solidification
This section is a horizontal line, indicating constant temperature. This represents a change of state: solidification, a transition from liquid to solid. The temperature remains constant at the solidification point (e.g., T = 25°C). We have two states of aggregation: liquid + solid.
Section 5: Temperature Decrease (Solid)
This section is a slanted line (going down), indicating a temperature decrease. We cool a solid, and it releases heat. Its particles do not move around each other. The forces of attraction between particles are very strong. The state of aggregation is solid.
The condensation point (which is also the boiling point in a heating graph) and the solidification point (which is also the melting point in a heating graph) are specific properties of matter.