7. How many joules of energy do I need to change 2 grams of water from 0°C solid water to 0° liquid water? A. 0 joules
B. 334 joules
C. 167 joules
D. 668 joules

8. How many grams of water can I covert from a liquid to a gas with 6768 joules?
A. 334 grams
B. 3 grams
C. 1 gram
D. 2,256 grams

7. D. 668 joules

8. B. 3 grams

Given

2 grams of water

6768 joules of energy

Required

Energy

Mass of water

Solution

The heat to change the phase can be formulated :

Q = m.Lf (melting/freezing)

Q = m.Lv (vaporization/condensation)

Lf=latent heat of fusion

Lv=latent heat of vaporization

7. phase change (ice to water)⇒Heat of fusion water=334 J/g

Q = 2 g x 334 J/g

Q = 668 J

8. phase change(water to vapor)⇒heat of vaporization water=2260 J/g

6768 J = m x 2260 J/g

m = 3 g

po-215 i got it right on the quiz

when the volume of gas is   changed from   717.73 ml   to 852 ml   the temperature will   change   from 315   c to 452   c

    calculation

this is calculated using the charles law formula

that is,   v1/t1 = v2/t2

          v1=?

        t1 = 315 c   into   kelvin = 315 +273 = 588 k

        v2 = 852   ml

        t2 = 425c + 273 =698 k

make v1   the subject of the formula ( by   multiplying both side by t1)

  v1=( v2 xt1) / t2

v1= (852 ml   x 588 k)/ 698 k= 717.73 ml