Question

How much heat energy in megajoules is neede to convert 7kilograms of ice at negative 9 degrees to water at 0 degrees celsius

Answer 1

Heat_1: Get the ice to 0 degrees

Convert 7 kg to grams

7 kg [1000 grams / 1 kg] = 7000 grams

Heat needed to get the the ice from - 9 to 0

deltat = 0 - -9 = 9 degrees

m = 7000 grams

c = 2.1 joules/gram

Heat_1 = m*c*deltat

Heat_1 = 7000 * 2.1 * 9

Heat_1 = 132,300 joules

Heat_2: Melt the ice.

There is no temperature change. The formula is 333 j/gram

Formula: H = mass * constant

H = 7000 g * 333 J / gram

H = 2331000 joules

Heat_3: Total amount of Joules needed.

2331000 + 132300 = 2 463 300 joules

Convert to Megajoules

2 463 300 joules * 1 megajoule / 1000000 = 2.63 megajoules.