Question

Help with sig fig!

Question: What is the pressure in a can at 1440 oC if the pressure at 47 oC is 103 kPa?

My answer: 19.265

What would be the correct sig fig?

Answer 1

how many significant figures do you have in 1440? How about in 47? 103?

Answer 2

103

Answer 3

Also, are you sure you have the right answer to start with? the pressure ought to be much higher at higher temperatures than it is at lower temperatures, no?

Answer 4

2 in 47, 3 in 103? @whpalmer4

Answer 5

Plugged in the equation: 103/173.5 (K) x 320.5(K) because I'm looking for p2.

Answer 6

3 in 1440? not too sure I just vaguely learned this yesterday

Answer 7

yes, agreed with the sig fig counts of 2,3,3 for 47, 103, 1440.

Answer 8

also with the indirect variation between pressure and temperature

Answer 9

So is my final answer correct and how do I determine the sig fig correctly?

Answer 10

@whpalmer4

Answer 11

temperature (measured in degrees Kelvin) and pressure are directly proportional (never mind that some idiot described the relationship as indirect variation earlier :-) If the temperature goes up, the pressure goes up. You've got an incorrect value for the temperature — 173.5 K is -100 C, but I don't see that figure anywhere in the problem.

As for significant figures, when multiplying or dividing, you use the smallest number of significant figures found in any of the numbers used. 2*3.1415926 = 6. unless you happen to know that 2 is an exact value, not subject to measurement error.

Answer 12

For a refresher or additional instruction on significant figures, I'm sure the Khan Academy videos are of the usual high standard: https://www.khanacademy.org/math/arithmetic/decimals/significant_figures_tutorial/v/significant-figures