# Chemistry P1 energetics question

## Recommended Posts

A pure aluminium block with a mass of 10 g is heated so that its temperature increases from 20 °C to 50 °C . The specific heat capacity of aluminium is 8.99 × 10–1 J g–1 K–1. Which expression gives the heat energy change in kJ?

A.      10 × 8.99 × 10–1 × 303

B.      10 × 8.99 × 10–1 × 30

C.     ( 10 × 8.99 × 10–1 × 303) / 1000

D.     ( 10 × 8.99 × 10–1 × 30) / 1000

The answer key says its D. I thought it was C. Why is it D?

using the formula

q=mc∆T

the ∆T  will be 50-20 = 30 'C and change to Kelvin so 273+30 = 303K

so isn't it

10 x 10 × 8.99 × 10–1 × 303 J and to change it to kJ I need to divide by 1000?

Since the specific heat capacity is given in K shouldn't I use Kelvin?

Thank you!!

##### Share on other sites

Hi!

Yes, you need to calculate the change in temp in kelvin, but that's what you did wrong

20 C = 293 K and 50 C= 323 K

So change in temp = 323-293 =30 K.

You might have noticed that this is the same as doing 50 C-20 C; the CHANGE in temperature in Kelvin is the same as the change in temperature in Celsius (very important to remember that this only applies to change in temperatures)

I hope this helped clarify your doubt

• 1

##### Share on other sites

@eross thank you very much!! It helped clarify my question.

## Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account. ×   Pasted as rich text.   Paste as plain text instead

Only 75 emoji are allowed.