Unit 2 - Energy from fuels

Question 1

What is the heat capacity of water?

Answer 1

4.18 kJ/kg/^oC (in databooklet page 3)

Question 2

Give the formula to calculate the heat energy

Answer 2

E= c x m x ΔT

Question 3

In the formula E= c.m.ΔT what is m? what is the unit for m?

Answer 3

m is the mass of the liquid heated in the experiment (NOT the mass of the fuel used) it is often water, and the mass need to be in kg.

Question 4

What is the mass in kg of 25cm³ of water?

Answer 4

0.025 kg

Question 5

What is the mass in kg of 2.3l of water?

Answer 5

2.3kg

Question 6

What is ΔT ?

Answer 6

Diffence/change in temperature (in degree celcius)

Question 7

A student did an experiment to find out the energy released by methanol.

He used 1.7g of methanol to heat up 100cm³ of water, the initial temperature was 23^oC and the final temperature was 63^oC.

Calculate the heat energy released by methanol.

Answer 7

E= c.m.ΔT

E= 4.18 x 0.1 x 40

E= 16.72 kJ

Question 8

A student find out the energy released by methanol from an experiment to be 12.3kJ.

He used 1.7g of methanol to heat up 80 cm³ of water,

The starting temperature was 22^oC.

Calculate the final temperature in the experiment done by the student.

Answer 8

E = c x m x ΔT

therefore ΔT = E / (c x m)

ΔT= 12.3 / (4.18 x 0.08)

ΔT= 36.8 ^oC

Starting temperature was 22^oC so the final temperature is: 22+ 36.8 = 58.8^oC

Question 9

Why the energy E, find by scientist is much higher than the one done in class?

Answer 9

Scientist use a BOMB calorimeter

or

In class, a lot of heat is lost to the surrounding

Question 10

What is the product of complete combustion of methanol?

Answer 10

water and carbon dioxide

Question 11

What is the test for water?

Answer 11

Cobalt chloride paper, blue paper that turns pink in the presence of water

Question 12

What is the test for Carbon Dioxide?

Answer 12

Carbon dioxide turns lime water cloudy

Question 13

What is the product for incomplete combustion of propanol?

Answer 13

Carbon MONOXIDE and water

Question 14

What is the term use to describe a chemical reaction that absorbs heat?

Answer 14

Endothermic reaction

Question 15

What is the term use to describe a chemical reaction that releases heat?

Answer 15

Exothermic reaction

Question 16

What is a fuel?

Answer 16

Chemical that burns to release energy

Question 17

Why do we use a copper can rather than a glass beaker in the experiment to find out the energy released by fuels?

Answer 17

Copper is a metal, it’s a better conductor of heat than glass.