Worksheet Heating Curve Of Water Answers

Worksheet: Heating Curve of Water – Answers and Explanations

Understanding the heating curve of water is crucial for grasping fundamental concepts in chemistry and physics, particularly concerning heat transfer, specific heat capacity, and phase changes. This comprehensive guide provides detailed answers and explanations for common worksheet questions on the heating curve of water, equipping you with a thorough understanding of this important scientific concept. We'll cover everything from basic definitions to more complex calculations and interpretations.

What is a Heating Curve?

A heating curve is a graph that illustrates the change in temperature of a substance as heat is added to it at a constant rate. The x-axis represents the heat added (often in Joules or kilojoules), while the y-axis represents the temperature (usually in degrees Celsius or Kelvin). The curve is not linear because the substance's temperature doesn't increase uniformly. This is due to the energy required for phase changes (melting, boiling, etc.).

Key Features of the Water Heating Curve

The heating curve of water displays several distinct regions:

1. Heating Solid Ice (Ice)

• Phase: Solid (Ice)
• Temperature Range: Below 0°C (32°F)
• Process: Heat energy is absorbed, increasing the kinetic energy of the water molecules within the ice lattice. This leads to a gradual increase in temperature. The slope of this section reflects the specific heat capacity of ice.

2. Melting Ice (Ice to Water)

• Phase Change: Solid to Liquid (Melting)
• Temperature: Constant at 0°C (32°F)
• Process: All the added energy is used to break the hydrogen bonds holding the water molecules together in the ice lattice. The temperature remains constant during this phase transition, even though heat is continually added. The amount of heat required is directly related to the heat of fusion of water.

3. Heating Liquid Water (Water)

• Phase: Liquid (Water)
• Temperature Range: 0°C to 100°C (32°F to 212°F)
• Process: Heat energy is absorbed, increasing the kinetic energy of the water molecules, leading to a gradual increase in temperature. The slope of this section reflects the specific heat capacity of liquid water.

4. Boiling Water (Water to Steam)

• Phase Change: Liquid to Gas (Vaporization/Boiling)
• Temperature: Constant at 100°C (212°F) at standard pressure.
• Process: All added energy is used to overcome the intermolecular forces holding the water molecules together in the liquid phase, allowing them to escape as steam (water vapor). The temperature remains constant during this phase transition. The amount of heat required is directly related to the heat of vaporization of water.

5. Heating Steam (Steam)

• Phase: Gas (Steam)
• Temperature Range: Above 100°C (212°F)
• Process: Heat energy is absorbed, increasing the kinetic energy of the water molecules in the gaseous phase, leading to a further increase in temperature. The slope of this section reflects the specific heat capacity of steam.

Common Worksheet Questions and Answers

Let's delve into common questions found in heating curve worksheets and provide detailed answers. These questions often involve calculations using the following formulas:

• Q = mcΔT: This formula calculates the heat (Q) required to change the temperature of a substance, where 'm' is the mass, 'c' is the specific heat capacity, and 'ΔT' is the change in temperature.

• Q = mL: This formula calculates the heat (Q) required for a phase change, where 'm' is the mass and 'L' is the latent heat (heat of fusion or vaporization).

Question 1: Describe the different phases and phase transitions represented on a heating curve of water.

Answer: The heating curve of water shows five distinct sections:

1. Solid (Ice): Ice below 0°C. Heat increases the kinetic energy of molecules.
2. Melting: At 0°C, ice melts into liquid water. Heat energy breaks intermolecular bonds. Temperature remains constant.
3. Liquid (Water): Liquid water between 0°C and 100°C. Heat increases kinetic energy, causing temperature to rise.
4. Boiling: At 100°C, liquid water boils into steam. Heat energy overcomes intermolecular forces, breaking them to form gas. Temperature remains constant.
5. Gas (Steam): Steam above 100°C. Heat increases the kinetic energy of steam molecules, increasing temperature.

Question 2: Explain why the temperature remains constant during phase transitions.

Answer: During phase transitions (melting and boiling), the added heat energy is not used to increase the kinetic energy (and thus the temperature) of the molecules. Instead, it's used to overcome the intermolecular forces holding the molecules together in their current phase. Once all the intermolecular forces are overcome, the temperature begins to rise again.

Question 3: Calculate the heat required to raise the temperature of 50g of ice from -10°C to 0°C. (Specific heat capacity of ice = 2.1 J/g°C)

Answer: Using the formula Q = mcΔT:

• m = 50g
• c = 2.1 J/g°C
• ΔT = 0°C - (-10°C) = 10°C

Q = (50g) * (2.1 J/g°C) * (10°C) = 1050 J

Question 4: Calculate the heat required to melt 50g of ice at 0°C. (Heat of fusion of water = 334 J/g)

Answer: Using the formula Q = mL:

• m = 50g
• L = 334 J/g

Q = (50g) * (334 J/g) = 16700 J

Question 5: Why is the slope of the liquid water section steeper than the slope of the steam section on the heating curve?

Answer: The slope of each section represents the specific heat capacity of that phase. Liquid water has a higher specific heat capacity than steam. This means that it requires more heat energy to raise the temperature of liquid water by 1°C compared to steam. A steeper slope indicates a lower specific heat capacity.

Question 6: A 100g sample of ice at -20°C is heated until it becomes steam at 120°C. Describe the changes that occur, and identify the energy changes involved in each stage.

Answer: The heating process involves several stages and energy changes:

1. Heating Ice: Heat is added to raise the temperature of the ice from -20°C to 0°C. This involves an increase in kinetic energy.
2. Melting Ice: Heat is added at a constant temperature of 0°C to melt the ice into liquid water. This involves overcoming the intermolecular forces (heat of fusion).
3. Heating Liquid Water: Heat is added to raise the temperature of the liquid water from 0°C to 100°C. This involves an increase in kinetic energy.
4. Boiling Water: Heat is added at a constant temperature of 100°C to convert liquid water into steam. This involves overcoming intermolecular forces (heat of vaporization).
5. Heating Steam: Heat is added to raise the temperature of the steam from 100°C to 120°C. This involves an increase in kinetic energy.

Each stage involves a specific heat capacity (except for melting and boiling), which determines how much heat is required to change the temperature for a given mass. The melting and boiling stages involve latent heat, requiring energy to change the phase without a temperature change.

Question 7: Explain the concept of specific heat capacity and its relevance to the heating curve.

Answer: Specific heat capacity is the amount of heat required to raise the temperature of 1 gram of a substance by 1°C (or 1 Kelvin). It's represented by 'c' in the formula Q = mcΔT. The steeper the slope of a section on the heating curve, the lower the specific heat capacity of the substance in that phase. Water's high specific heat capacity is responsible for its ability to moderate temperature fluctuations.

Question 8: Explain the concept of latent heat and its relevance to the heating curve.

Answer: Latent heat is the heat energy required to change the phase of a substance without a change in temperature. The heating curve shows this as plateaus during melting (heat of fusion) and boiling (heat of vaporization). This energy is used to break intermolecular bonds and overcome the forces holding the molecules in their current phase.

Question 9: How would the heating curve change if the heating rate were increased?

Answer: Increasing the heating rate would not change the overall shape of the heating curve – the flat sections (phase transitions) would still be present at the same temperatures. However, the time taken to reach each point on the curve would be reduced. The slopes of the non-horizontal sections would become steeper.

Question 10: How would the heating curve change if a different substance were used instead of water?

Answer: The heating curve would have a different shape because different substances have different specific heat capacities and latent heats. The melting and boiling points would be different, resulting in plateaus at different temperatures. The slopes of the sections representing heating would also be different.

By carefully analyzing these questions and answers, you can gain a comprehensive understanding of the heating curve of water and its underlying principles. Remember to practice solving various problems using the provided formulas to solidify your knowledge. This will not only improve your understanding of heating curves but also enhance your problem-solving skills in thermodynamics and related fields. Good luck with your studies!