"Heat Calculations q = " mini-practice

How many Joules, J, of energy are required to completely melt 100 grams of solid water at 0 °C ?

• 418 J

• 41800 J

• 33400 J
• 0 J

Tags

NGSS.HS-PS3-1

How many Joules of heat are needed to increase the temperature of 50.0 grams of liquid water from 20 Celsius to 60 Celsius?

• 16700 J

• 113000 J

• 2000 J

• 8360 J

• 668000 J

Tags

NGSS.HS-PS3-1

How many Joules are required to boil 75 grams of water at 373 K ?

(Hint... beware of unnecessary information)

• 25,050 J

• 169,500 J

• 31,350 J

• 63,223,500 J

Answer explanation

again, there is a phase change word , "boil". Thus, the temperature it occurs at (373 K) is irrelevant to the math. (There is no CHANGE in temperature when something boils)

You have to decide between using

q = mH_f and q = mH_v

H_v , 2260 J/g, relates to phase changes between liquid and gas states. This is what you use.

q = 75 g x 2260 J/g = 169500 J

Tags

NGSS.HS-PS3-1

NGSS.HS-PS3-4

How much energy is absorbed by a substanct to increase its temperature by 25 degrees Celsius if its mass is 60.0 grams and its specific heat capacity is 1.50 J/g C?

(specific heat capacity is the c of q=mcΔT)

• 2250 J
• 1800 J
• 3000 J
• 1500 J

Answer explanation

q = mcΔT

q = 60.0 g x 1.50 J/g C x 25 degrees C

= 2250 J

Tags

NGSS.HS-PS3-1