April 18, 2015

Homework Help: chemistry

Posted by Fido on Sunday, October 22, 2006 at 6:07pm.

Can specific heat be negative? I know energy can be (as in joules or calories) because when something cools down the temperature difference is a negative, and because the energy is an important part of the formula for specific heat, couldn't it be negative?

Specific heat content is defined as the heat required to raise a given mass 1 deg C. It takes real heat (+) to increase temperature, in accordance with the Kinetic Molecular theory.

Then how come calories and joules (as in energy) can be negative?

We learned this formula for cp.

cp of object 2=m(water) * temp. difference (water) * cp (water)% m (object 2) * temp. difference (object 2)

What if the temperature difference is negative for either the water or the object? Wouldn't the cp come out negative?

That is not the definition of specific heat capacity. This formula is exactly wrong. Let me show you.

In any reaction, the sum of the heat gains is zero. Some will lose heat (negative gain), and some will gain.

Heatgainedbywater+ heatgainedbyboject=0

Now if you solve this, it is always correct. Your teacher probably did the old (wrong) Heat gained= heat lost

But this is NOT right what is right is
absolutevalue Heatgained=absolutevalue Heat lost. When you solve it for cp, you get your formula, but you dropped the absolute values signs, making the problem you suggest: how to handle signs.

Heat capacity is always positive.

Thanks, but I should probably do it the way my teacher taught me to. And I guess I'll just drop the negative.

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