3. Matter and Energy
Heat Capacity
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Here it says, how much heat in kilojoules is released when 120 grams of water goes from 90 degrees Celsius to 45 degrees Celsius. The specific heat capacity of water is given as 4.184 joules over grams times degrees Celsius. So So we need to determine the heat which is q, they're giving us here the mass of the water which is m, we have our change in temperature here, and we have our specific heat capacity which is lowercase c. So q equals m cap, plug in the grams of water given to us, plug in the specific heat capacity that's given to us, and remember the units for the specific heat capacity dictate the units for temperature. Since this is in Celsius it's good to have our temperatures in Celsius as well. Delta t is final minus initial. So when we do all that, Celsius cancel out, grams cancel out, and we'll have joules of heat involved. When we plug that in, we're gonna get here negative 22593 0.6 joules. But here we want the answer in kilojoules, so 1 kilojoule is equal to 10 to the 3 joules. So here joules cancel out and we'll have kilojoules at the end. So that comes out to negative 22 0.5936 kilojoules. Here, this has 4 sig figs, 1 sig fig, 2 sig figs. Specific heat capacity we could use it since it's given to us as a value, but we don't have to. Here we could just go with 1 sig fig, but I feel like that's too much rounding, so let's just go with 2 sig figs based on 45. So it's gonna be negative 23, roughly, kilojoules of heat are released. So here using q equals mcat we're able to isolate the heat that's involved in the releasing by the water molecule going from 90 degrees Celsius to 45 degrees Celsius.
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