2.1 Thermochemistry

Question 1

exothermic

Answer 1

A reaction that releases energy in the form of heat to its surroundings, there is no temperature rise and deltaH is negative

Question 2

Endothermic

Answer 2

A reaction that ABSORBS energy in the form of heat from its surroundings , there’s a temperature drop and deltaH is positive.

Question 3

describe an experiment to measure enthalpy change for simple reactions between a solid and a aqueous solution eg Zn and CuSO4 between HCl and NaOH.

Answer 3

• Measure an appropriate volume of acid using a burette or pipette and place into polystrene cup
• has to be in excess to ensure all solid reacts
• use thermometer to measure initial temp
• accurately weigh solid in powder form and add into cup
• keep stirring with thermometer and record temp untill constant achieved
• plot a graph of temperature against time to calculate max te,[erature
• Use Q=mcE=mc∆T and ∆T= -q/n

Question 4

How do you measure enthalpy change

Answer 4

Change in heat = heat in products - heat in reactants

Question 5

Definition of standard enthalpy change of reaction

Answer 5

Enthalpy change in any reaction between the number of moles of reactants shown in the equation for the reaction

Question 6

Define standard enthaply of formation

Answer 6

Enthalpy change when 1 mole of a substance is formed from its elements in their standard states under standard conditions.

Question 7

Define standard enthalpy of combustion

Answer 7

Enthalpy change when 1 mole of a substance is completely burned (combusted) in oxygen under standard conditions

Question 8

What’s hess’s law

Answer 8

States that the total enthalpy change for a reaction is independent of the route taken

Question 9

What does average bond enthalpy mean?

Answer 9

** the energy required to break one mole of a bond in a gaseous species under standard conditions.**

Question 10

Why are energy change reactions carried out in an insulated container

Answer 10

To prevent heat energy loss to the surroundings.