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In this lesson, we will learn how to use the formula E = mL to calculate the amount of energy absorbed or released by a change in the state of a material.

Q1:

1 kg of copper and 1 kg of nickel are both heated continuously at the same rate. Determine which metal will completely melt first. Use a value of 205 kJ/kg for the specific latent heat of fusion of copper and use a value of 297 kJ/kg for the specific latent heat of fusion of nickel.

Q2:

Which of the following is the correct unit for the specific latent heat of fusion?

Q3:

Water in a pan reaches 1 0 0 ∘ C , but the pan is still left on the heat, so eventually all of the water turns to water vapor. Calculate the energy needed to evaporate the 1.2 kg of water contained by the pan. Use a value of 2 2 5 8 kJ/kg for the specific latent heat of vaporization of water. Give your answer to 2 significant figures.

Q4:

Which of the following is the correct formula for the energy required to evaporate a substance? 𝐸 represents the energy required, 𝑚 represents the mass of the substance, 𝐿 represents the specific latent heat of vaporization, 𝑐 represents the specific heat capacity, and Δ 𝜃 represents the change in temperature.

Q5:

A forge can transfer 200 kJ of energy to a metal to heat it before running out of fuel. Bars of silver or gold can be placed in the forge to melt them. If the metal to be melted is already at its melting temperature when placed in the forge, determine how much more gold than silver the forge can melt before running out of fuel. Use a value of 63 kJ/kg for the specific latent heat of fusion of gold and use a value of 111 kJ/kg for the specific latent heat of fusion for silver. Give your answer to 2 significant figures.

Q6:

A 10 g cube of ice at 0 ∘ C is placed outside in direct sunlight on a hot day. The sunlight and the hot air around the cube heat it at a rate of 10 W. It takes 5.56 minutes for the ice to completely melt. Calculate the specific latent heat of fusion for water. Give your answer to 3 significant figures.

Q7:

A pan is filled with 2 kg of water at a temperature of 1 0 0 ∘ C . If the pan can transfer energy to the water at a rate of 2.5 kW, determine how many minutes it will take to vaporize all of the water in the pan. Use a value of 2 2 5 8 kJ/kg for the specific latent heat of vaporization of water. Give your answer to the nearest minute.

Q8:

A 10 kg block of ice is converted to water vapor. The block of ice starts at − 2 0 ∘ C ; first, it must be completely melted, and then it is heated to 1 0 0 ∘ C . Find the energy required to do this. Use a value of 2 1 0 8 / ⋅ J k g C ∘ for the specific heat capacity of ice and use a value of 4 1 8 4 / ⋅ J k g C ∘ for the specific heat capacity of water. Use a value of 334 kJ/kg for the latent heat of fusion of water and use a value of 2 2 5 8 kJ/kg for the latent heat of vaporization of water. Give your answer to 3 significant figures.

Q9:

30 g of molten gold is allowed to solidify. It releases 1 8 9 0 J of energy to the surrounding environment as it does so. What is the specific latent heat of fusion for gold?

Q10:

A metal at the temperature at which it melts is heated until all of the metal has become liquid. It takes 41 kJ to completely melt the metal, and its mass is 0.2 kg. What is the specific latent heat of fusion of the metal?

Q11:

565 kJ of energy is used to melt a block of zinc that was already at its melting temperature when the energy was supplied to it. Find the mass of the block of zinc, using a value of 113 kJ/kg for the specific latent heat of fusion of zinc.

Q12:

A substance, which is initially at 2 0 ∘ C and solid, is heated. The temperature of the substance is recorded over time, and this data is shown in the graph.

What is the melting point of the substance?

Q13:

Determine how much energy is needed to melt 2 kg of ice. Use a value of 334 kJ/kg for the specific latent heat of fusion of ice.

Q14:

The table lists the specific latent heat of fusion for various metals. You have 200 g of an unknown metal. You heat the metal to its melting point and then measure how much energy is released for all of it to melt, and you get a value of 79.6 kJ. Which of the four metals listed in the table do you have?

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