Specific Latent Heat

Which of the following describes a phase transition from a gas to a liquid?

a) Boiling.

b) Evaporation.

c) Deposition.

d) Condensation.

d

True or False: It is impossible for a substance to transition directly from a solid to a gas.

False

A glass of water is heated such that it begins boiling into steam. What is happening to the water’s temperature during this phase transition?

a) It’s increasing.

b) It’s decreasing.

c) It isn’t changing.

d) Not enough information.

c

Which of the following is the best description of “latent heat”?

a) The energy needed to heat a substance.

b) The energy needed for a phase transition.

c) The heat given off by a substance.

d) The energy a substance releases when cooling.

b

True or False: The specific latent heat is the energy required for 1kg of a particular substance to complete a particular phase transition.

True

What name do we use for the latent heat of a transition between solids and liquids?

a) Fusion.

b) Fission.

c) Vaporisation.

d) Melting.

a

Why is there no change in temperature during a phase transition, even if energy is supplied to the system?

a) The extra energy is used to break bonds to cause the phase transition.

b) The extra energy turns into kinetic energy, not thermal energy.

c) During a phase transition, the system doesn’t absorb any energy.

d) The energy is converted into mass, which is how either liquid or gas is created.

a

The specific latent heat of fusion of water is 334 kJ/kg and for ethanol it is 108 kJ/kg. When the melting point is reached, it takes more energy to melt ethanol than it does to melt water.

False

Ammonia has a specific latent heat of fusion of 332 kJ/kg. How much energy does it take to melt 1 g of ammonia which is already at its melting point?

322J

The specific latent heat of fusion is smaller than the specific latent heat of vaporisation for a specific material. What does this statement mean?

a) Gas particles have less kinetic energy than liquid particles.

b) Solids are the most likely form for a material to be in at room temperature.

c) It takes more energy to melt a material than to boil it.

d) It takes more energy to boil a material than to melt it.

d

define the term, phases of matter.

Phases of matter describe what is happening to the particles of a substance (e.g., solids, liquids, gases).

Define the term, phase transitions.

Phase transitions refer to transitions between the states of matter (aka phases of matter).

What happens in a phase transition?

During a phase change, temperature remains constant. All additional energy goes to potential energy for the transition

Define the term, latent heat.

Latent heat is the amount of energy required to transition from one phase to another.

Define the term, specific latent heat.

Specific latent heat is the amount of energy required to transition 1kg of a specific substance from one phase to another.

Recall the equation for specific latent heat.

Q = mL

Fill in the blanks: Specific latent heat can differ drastically for the same substance but _____ _____.

Specific latent heat can differ drastically for the same substance but different transitions.

Define the term, latent heat of fusion.

Latent heat of fusion refers to the energy required to melt a kilogram of material.

Define the term, latent heat of vaporisation.

Latent heat of vaporisation refers to the energy required to boil a kilogram of material.

Complete the following sentence: The specific latent heat of fusion is the phase transition between a …

solid and liquid.

Complete the following sentence: The specific latent heat of vaporisation is the phase transition between a …

liquid and gas.

What is the formula used for calculating the energy required to cause a phase transition of a material?

Q = mL

The specific latent heat of fusion for water is 3.34×10⁵ Jkg⁻¹. How much energy is required to convert 0.4 kg of ice at its melting point to liquid water?

133,600J

The specific latent heat of vaporisation for benzene is 3.94×10⁵ J kg⁻¹.

How much energy is required to convert 0.750 kg of liquid benzene at its boiling point to vapour, correct to 3 significant figures?

296 × 10³ J

The specific latent heat of fusion for gold is 6.4×10⁴ Jkg⁻¹.

How much energy is required to convert 500g of solid gold at its melting point to a liquid?

32,000J

The specific latent heat of vaporisation for ethanol is 8.55×10⁵ J kg⁻¹.

How much energy is required to convert 1500 g of liquid ethanol at its boiling point to vapour, correct to 3 significant figures?

1280 × 10³ J

It takes 75,600 J of energy to melt a 0.2 kg sample of aluminium at its melting point.

What is the specific latent heat of fusion for aluminium?

3.78 × 10⁸ Jkg^-1

It takes 840 kJ of energy to vaporise a 0.60 kg sample of ammonia at its boiling point.

What is the specific latent heat of vaporisation for ammonia, correct to 2 significant figures?

1,400,000 Jkg^-1

Chantel wrote a list of the steps to follow when finding the energy required to convert a solid substance at its melting point into a vapour.

1. Calculate the energy required to heat the solid.

2. Calculate the energy required to heat the liquid.

3. Calculate the energy required to convert from a liquid to a vapour.

4. Add the energies together.

Which step contains a mistake?

Step 1

The specific latent heat of vaporisation for water is 2.26×10⁶J kg⁻¹ and its specific latent heat of fusion is 3.34×10⁵J kg⁻¹. The specific heat capacity of liquid water is 4.18×10³ J kg⁻¹ K⁻¹.

Calculate the amount of energy that needs to be removed from 0.75 kg of water to convert it from a vapour at 100°C to ice at 0°C.

2,259,000J

The specific latent heat of fusion for copper is 1.34×10⁵J kg⁻¹ and its specific latent heat of vaporisation is 5.07×10⁶J kg⁻¹. The specific heat capacity of liquid copper is 390 J kg⁻¹ K⁻¹. Copper melts at 1083°C and boils at 1187°C.

What is the energy required to convert 0.5 kg of copper from a solid at its melting point to a vapour at its boiling point, correct to 3 significant figures?

2,620,000J