Answer:
Step-by-step explanation:
To solve this problem, we need to use the equation Q = mcΔT, where Q is the heat transfer, m is the mass of the water, c is the specific heat capacity of water, and ΔT is the change in temperature.
First, we need to determine the mass of water in the pot. Let's assume that the pot has a volume of 1 liter, or 1000 mL. Water has a density of 1 g/mL, so the mass of the water is 1000 g.
Next, we need to determine the change in temperature of the water. We know that the heat transfer is 640 KJ, and the specific heat capacity of water is 4.184 J/g°C. So, the change in temperature of the water is 640,000 J / (4.184 J/g°C * 1000 g) = 152.3°C.
Now, we can use the equation Q = mcΔT to solve for the mass of propane needed. We know that Q = 640,000 J, m = 1000 g, c = 4.184 J/g°C, and ΔT = 152.3°C. Plugging these values into the equation, we get 640,000 J = (1000 g)(4.184 J/g°C)(152.3°C). Solving for the mass of propane, we get m = 640,000 J / (4.184 J/g°C * 152.3°C) = 30.8 g.
So, the amount of propane needed to transfer 640 KJ of heat into the pot of water is 30.8 g.