How many moles of liquid water must freeze to remove 100 kJ of heat? (ΔHf = –334 J/ g.

1 answer:

5 0

First figure out how many grams must freeze and then convert the grams to moles.
Hf = -334 J/g. Convert this to KJ/g by dividing by 1000. (There are 1000 Joules in a kJ). 
Hf = -334 J/g ÷ 1000 J/kj = -0.334 kJ/g 
Now, divide 100 kJ by -0.334 kJ/g (see how the units are lining up?) 
100 kJ ÷ -0.334 kJ/g = 299 g 
Now convert this to moles by dividing by the molecular weight of water (18.0g/mole). 
299 ÷ 18.0 = 16.6 moles

You might be interested in

Labels of many food products have expiration dates, at which point they are typically removed from the supermarket shelves. A pa

White raven [17]

Answer:

Explanation:

Since it first order, we use order rate equation

In ( $\frac{A1}{A0}$ ) = -kt where A1 is the final quality = 0.8 (80%), A0 is the initial quality = 1 ( 100%)

also, t half life = $\frac{In2}{k}$ where k is rate constant

k = $\frac{In 2}{45 days}$ = 0.0154

In ( $\frac{0.8}{1}$ ) = - 0.0154 t

-0.223 / -0.0154 = t

t = 14.49 approx 14.5 days from the date the yogurt was packaged

6 0

3 years ago

If a substance has a half life of 58 years and starts with 500 g radioactive, how much remains radioactive after 30 years?

Vilka [71]

Answer:

A = 349 g.

Explanation:

Hello there!

In this case, since the radioactive decay kinetic model is based on the first-order kinetics whose integrated rate law is:

$A=Ao*exp(-kt)$

We can firstly calculate the rate constant given the half-life as shown below:

$k=\frac{ln(2)}{t_{1/2}} =\frac{ln(2)}{58year}=0.012year^{-1}$

Therefore, we can next plug in the rate constant, elapsed time and initial mass of the radioactive to obtain:

$A=500g*exp(-0.012year^{-1} *30year)\\\\A=349g$

Regards!

5 0

3 years ago

I need part 1 and 2 please , just separate answers

Vladimir79 [104]

First, we have to remember the molarity formula:

$M=\text{ }\frac{moles\text{ of solute}}{L\text{ solution}}$

Part 1:

In this case, our solute is sodium nitrate (NaNO3), and we have the mass dissolved in water, then we have to convert grams to moles. For that, we need the molecular weight: