C3f - Energy

Question 1

Describe exothermic reactions(3)

Answer 1

one in which energy is transferred into the surroundings; (releases energy in the form of heat)
-amount of energy released in bond formation > amount of energy taken in to break bonds

shown by a rise in temperature of the surroundings

Question 2

Describe endothermic reactions(3)

Answer 2

one in which energy is taken from the surroundings; (absorbs energy in the form of heat)
-amount of energy taken in to break bonds > amount of energy released in bond formation

shown by a fall in temperature of the surroundings

Question 3

Describe a simple calorimetric method for comparing the energy transferred per gram of fuel burned (5)

Answer 3

use of spirit burner to heat water in a copper calorimeter above it

measure mass of fuel burnt

measure temperature change

fair and valid tests by controlling variables

repeat test for results to be reliable

Question 4

What are the controlled variables in calorimetry(2)

Answer 4

height of calorimeter over the flame

volume of water used

Question 5

What are the dependent variables in calorimetry

Answer 5

temperature change

Question 6

What are the independent variables in calorimetry

Answer 6

fuel used

Question 7

What is the formula to find energy transferred in joules

Answer 7

Q=mcΔt

Energy transferred(J) = Mass of water heated x temperature change x specific heat capacity(4.2)

Question 8

Formula to find energy transferred in joules per gram of fuel

Answer 8

energy transferred per gram of fuel (J/g) = energy released (J) / mass of fuel burned (g)