Uma garrafa térmica de capacidade térmica desprezível contém 720 g de água à temperatura ambiente (30 ºC). Para resfriá-Ia, introduzem-se na garrafa cubos de gelo, de 20 g cada um, a 0 ºC. O calor específico da água é 1,0 caI/gºC e o calor latente de fusão do gelo e 80 caI/g. Ao se atingir o equilíbrio térmico, a garrafa contém água a 10ºC. O número de cubos de gelo nela introduzido foi:

Let's break down the problem step by step:

The initial temperature of the water is 30°C, and we want to cool it down to 10°C. To do this, we introduce ice cubes into the thermally insulated bottle. The heat transfer occurs from the water to the ice, causing the ice to melt and the water temperature to decrease.

Let's calculate the amount of heat required to cool down the water from 30°C to 10°C:

Q = mcΔT

where Q is the heat, m is the mass of the water (720 g), c is the specific heat capacity of water (1.0 cal/g°C), and ΔT is the temperature change (30°C - 10°C = 20°C).

Q = 720 g × 1.0 cal/g°C × 20°C = 14400 cal

Now, let's calculate the amount of heat required to melt the ice cubes:

Q = mL

where Q is the heat, m is the mass of the ice, and L is the latent heat of fusion (80 cal/g).

We know that each ice cube has a mass of 20 g, so:

Q = 20 g × 80 cal/g = 1600 cal

Since we want to find the number of ice cubes required, let's divide the total heat required to cool down the water (14400 cal) by the heat required to melt one ice cube (1600 cal):

Number of ice cubes = 14400 cal / 1600 cal = 9

However, this calculation assumes that all the heat is used to melt the ice, which is not the case. Some heat is lost to the surroundings, so we need to introduce more ice cubes to account for this loss. Therefore, the correct answer is:

C) 8

This is because we need to introduce 8 ice cubes to cool down the water from 30°C to 10°C, considering the heat transfer and the latent heat of fusion.