(a) (i) Explain latent heat.
(ii) State two factors that affect the rate of evaporation of a liquid
(a)
(i) Latent heat is the amount of heat energy required to change the state of a substance without changing its temperature. This means that the energy is either absorbed or released during a change in state, such as during melting, evaporation, or condensation.
(ii) The rate of evaporation of a liquid is affected by two main factors: temperature and surface area. As temperature increases, the rate of evaporation increases because more energy is available to break the bonds between liquid molecules. A larger surface area also increases the rate of evaporation because more liquid molecules are exposed to the air, allowing for more frequent collisions and evaporation.
(b)
(i) Water in a clay pot is cooler than water in a closed plastic container on a dry day because of evaporation. The porous surface of the clay pot allows for water to seep through and evaporate, which removes heat from the remaining water and causes it to cool. In contrast, a closed plastic container does not allow for evaporation, so the water remains at the same temperature.
(ii) Food gets cooked faster in a pressure cooker than in an ordinary cooking pot because of increased pressure and temperature. When the pressure is increased in a sealed container, the boiling point of water increases, which means that food can be cooked at a higher temperature. This higher temperature allows for faster cooking because it breaks down the food faster and more thoroughly.
(c)
Two effects of heat on a substance are expansion and change in state. When a substance is heated, its particles gain more energy and move faster, causing them to spread out and take up more space, leading to expansion. Also, when heat is added or removed from a substance, it can change its state from solid to liquid or from liquid to gas, or vice versa.
(d)
(i) The latent heat of fusion of the body can be calculated using the formula Q = mL, where Q is the heat energy required, m is the mass of the substance, and L is the latent heat of fusion. First, we need to calculate the heat energy required to melt the body: Q = VIt = (40V)(12A)(1400s) = 6.72 x 10^6 J. Next, we need to calculate the heat energy required to raise the temperature of the body by 60°C: Q = mcΔT = (1.5kg)(4200 J/kg°C)(60°C) = 3.78 x 10^5 J. Therefore, the total heat energy required is 7.08 x 10^6 J. Since the heat energy required for melting is equal to the product of the mass and latent heat of fusion, we can calculate the latent heat of fusion as L = Q/m = (6.72 x 10^6 J)/(1.5 kg) = 4.48 x 10^6 J/kg.
(ii) The specific heat capacity of the body can be calculated using the same formula as before, Q = mcΔT, where Q is the heat energy required, m is the mass of the substance, c is the specific heat capacity, and ΔT is the change in temperature. We know that the heat energy required to raise the temperature of the body by 60°C is 3.78 x 10^5 J, and we know that the mass of the body is
