Question

unit 3 worksheet 4 - quantitative energy problems
part 2
energy constants (h₂o)
334 j/g heat of fusion (melting or freezing) hf
2260 j/g heat of vaporization (evaporating or condensing) hv
2.1 j/g°c heat capacity (c) of solid water
4.18 j/g°c heat capacity (c) of liquid water
for each of the problems sketch a warming or cooling curve to help you decide which equation(s) to use to solve the problem. keep a reasonable number of sig figs in your answers.

1. how much energy must be absorbed by a 150 g sample of ice at 0.0°c that melts and then warms to 25.0°c?
2. suppose in the icy hot lab that the burner transfers 325 kj of energy to 450 g of liquid water at 20.°c. what mass of the water would be boiled away?

Explanation:

Step1: Calculate the energy required to heat the water from \(20^{\circ}C\) to \(100^{\circ}C\)

Use the formula \(Q = mc\Delta T\), where \(m = 450\space g\), \(c=4.18\space J/g^{\circ}C\), and \(\Delta T=100 - 20=80^{\circ}C\)

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Step2: Calculate the energy available for vaporization

The total energy \(Q_{total}=325\space kJ\). The energy for vaporization \(Q_v=Q_{total}-Q_1\)

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Step3: Calculate the mass of water vaporized

Use the formula \(Q = mH_v\), where \(H_v = 2260\space J/g\). Rearranging for \(m\) gives \(m=\frac{Q}{H_v}\)

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Answer:

\(77\space g\) (rounded to two significant figures)