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Rufina [12.5K]
3 years ago
13

Name each activity or observation as either physical or chemical change.

Chemistry
1 answer:
OLga [1]3 years ago
8 0
<span>1) Boiling water for pasta-> physical
2) Digesting food -> chemical
3) Soda goes "flat" -> physical
4) Stretching a rubber band -> physical
5) Grilling a hamburger -> chemical
6) Adding sugar to tea -> physical
7) Adding lemon to tea -> physical
8) Mowing the grass -> physical
9) The smell of perfume "wafts" across the room -> physical
10) Candle wax melts -> physical
11) Breaking glass-> physical
12) Making cement-> chemical
13) Lighting a match-> chemical
14) Water is absorbed by a paper towel-> physical
15) Firefly glows in the dark-> chemical
16) Snow melts-> physical
17) Bleaching your hair-> chemical
18) Turning on a light bulb-> physical
19) Milk goes sour-> chemical
20) Shooting off fireworks-> chemical</span>
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What fraction of a Sr-90 sample remains unchanged after 87.3 years
jolli1 [7]
The answer is 1/8.

Half-life is the time required for the amount of a sample to half its value.
To calculate this, we will use the following formulas:
1. (1/2)^{n} = x,
where:
<span>n - a number of half-lives
</span>x - a remained fraction of a sample

2. t_{1/2} = \frac{t}{n}
where:
<span>t_{1/2} - half-life
</span>t - <span>total time elapsed
</span><span>n - a number of half-lives
</span>
The half-life of Sr-90 is 28.8 years.
So, we know:
t = 87.3 years
<span>t_{1/2} = 28.8 years

We need:
n = ?
x = ?
</span>
We could first use the second equation, to calculate n:
<span>If:
t_{1/2} = \frac{t}{n},
</span>Then: 
n = \frac{t}{ t_{1/2} }
⇒ n = \frac{87.3 years}{28.8 years}
⇒ n=3.03
<span>⇒ n ≈ 3
</span>
Now we can use the first equation to calculate the remained amount of the sample.
<span>(1/2)^{n} = x
</span>⇒ x=(1/2)^3
⇒x= \frac{1}{8}<span>
</span>
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How would one convert 6 pounds to ounces (16 oz = 1b)?
NNADVOKAT [17]

Answer:

D.

Explanation:

I just got it right in the test :)

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1. by making a atomic configuration
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