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shtirl [24]
3 years ago
8

78.9 + 890.43 - 21 = 9.5 x 10^2

Chemistry
1 answer:
maria [59]3 years ago
8 0

948 or 9.48 x 10^2

There are two sets of rules for significant figures

• One set for addition and subtraction

• Another set for multiplication and division

You used the set for multiplication and division.

This problem involves addition and subtraction, and the rule is

The number of places after the decimal point in the answer must be <em>no greater than the number of decimal places in every term</em> in the sum.

Thus, we have

78.9

+890.43

-21.

= 948.33

The "21" term has the fewest digits after the decimal point (none), so the answer must have no digits after the decimal point.

To the correct answer is 948 = 9.48 x 10^2. It has three significant figures.

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What is the energy change if 84.0 g of calcium oxide (CaO) reacts with excess water in the following reaction?
pochemuha
   The energy change  if 84.0 g   of CaO  react  with  excess  water is  98KJ of heat is released.

calculation
heat  =  number of moles  x  delta H

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Heat is therefore =  1.5 moles  x -65.2 = - 97.8 Kj = -98 Kj

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