Question

1. how much work is done in joules (j) when 818.5 j of heat was released, resulting in a system change of 1725 j? choose the answer.
2. is this work done on or by the system? why? write this answer for practice on your practice sheet.

definitions and standards: 1000 j = 1 kj, d = delta, dt = change in temperature (°c), dhvap = heat of vaporization (j/g), dhfus = heat of fusion (j/g), s = specific heat (j/g°c), s water = 4.184 j/g°c, s steam = 2.02 j/g°c, s ice = 2.05 j/g°c, dhfush2o = 334 j/g, dhvaph2o = 2260 j/g, ccalorimetry = heat capacity (kj/°c)
formula bank: 1. q = m·c·δt q = m·s·δt 2. q = c·δt 3. qvap = m·δhvap 4. qfus = m·δhfus 5. δh°rxn = σ(δhfprod) - σ(dhfreact) 6. δu = q + w δe = q + w 7. w = δu - q w = δe - q 8. w = -p·δv

Explanation:

Step1: Identify the formula

Use the formula \( \Delta U=q + w\), where \( \Delta U\) is the change in internal energy of the system, \(q\) is the heat, and \(w\) is the work. Rearranged for \(w\), we get \(w=\Delta U - q\).

Step2: Substitute the values

Given \( \Delta U = 1725\space J\) and \(q=- 818.5\space J\) (negative because heat is released).

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Step3: Determine the work - system relationship

Since \(w>0\), the work is done on the system. When \(w>0\), the energy is transferred into the system as work. This means that an external force is compressing the system (for example, in a piston - cylinder arrangement) or some other form of work input is occurring.

Answer:

1. \(2543.5\space J\)
2. The work is done on the system. Because \(w = 2543.5\space J>0\). When \(w>0\), energy is transferred into the system as work.