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

What mass of liquid water can you increase the temperature by 20 °C if you add 20,000 J of heat?

• 250 g
• 105 g
• 240 g
• 350 g

Tags

NGSS.HS-PS3-1

NGSS.HS-PS3-4

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 released when 350 grams of water freeze at 0 °C

• 791,000 J

• 0 J

• 116,900 J

• 399,399J

Answer explanation

freezing, like melting, is a phase change between solid and liquid states.

Thus, it is a q = mH_f problem

Simply solving for q.

q = 350 g x 334 J/g = 116,900 J

Tags

NGSS.HS-PS3-1

What is the change in temperature, (ΔT) when 50,000 Joules of energy is absorbed by 200. grams of water?

(hint: Treat ΔT as you would any of the other components to the formula q = mCΔT)

• 16.0 °C

• 150 °C

• 59.8 °C

• 4.00 °C

Tags

NGSS.HS-PS3-1

How many Joules of heat are needed to increase the temperature of 50.0 grams of liquid water by 40.0 degrees?

(hint... use q = mCΔT)

• 16700 J

• 113000 J

• 2000 J

• 8360 J

• 668000 J

Tags

NGSS.HS-PS3-1