Keith Chan
Physics Lab T1 Conservation of Thermal Energy Weight of cup to hold cold water: 0.00293 kg Weight of tap water w/ cup: 0.07733 kg Weight of cup to hold hot water: 0.00236 kg Weight of hot water w/ cup: 0.08590 kg Temperature of tap water: 18 oC Temperature of hot water: 83 oC Final temperature : 48 oC Weight of mixture: 0.15824 kg Internal energy gain by cold water = (mc△T)cold water = (0.0773 – 0.00293)(4200)(48 – 18) = 9370.62 Jkg-1oC Internal energy loss by hot water = (mc△T)hot water = (0.08590 – 0.00236)(4200)(83 – 48) = 12280.38 Jkg-1oC In an ideal case, all internal energy loss by the hot water should be transferred to the cold water and heat it up. However, the results from our experiment shows that the energy loss by hot water is greater than the energy gain by cold water meaning that some of the internal energy loss by hot water is not transferred to the cold water (i.e. not all energy is used to heat up the cold water). There are a few possible reasons for this: 1. Some internal energy is loss when water evaporates. As water evaporates, molecules with higher energy will ‘escape’ as water vapor. Therefore, the remaining total energy of the mixture decreases. The lid which stops some water vapor from escaping, yet after the steam condenses on the lid, the energy is absorbed by the lid and drips back to the mixture at a lower temperature. 2. There is constant heat loss to the surrounding throughout the experiment. For instance, pouring hot water to cold water exposes the hot water to room temperature. Heat is loss to the environment by radiation and conviction as a result of the temperature difference.
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