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Flashcards in Chains, Energy and Resources - Energy Deck (81):
1

Define chemical energy.

Chemical energy is a special form of potential energy that lies within chemical bonds.

2

Define enthalpy.

Enthalpy is the heat content that is stored in a chemical system.

3

What letter or symbol is used to represent enthalpy?

The letter H is used to represent enthalpy.

4

Define the chemical system.

The chemical system is the reactants and products.

5

Define the surroundings.

The surroundings are what is outside the chemical system.

6

Define the enthalpy change.

Enthalpy change, ΔH, is the heat exchange with the surroundings during a chemical reaction at constant pressure.

7

What is the symbol for the enthalpy change?

The symbol for enthalpy change is ΔH.

8

What type of reaction releases heat?

An exothermic reaction releases heat.

9

Which type of reaction absorbs heat?

An endothermic reaction absorbs heat.

10

Define exothermic.

Exothermic refers to a reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings.

11

Define enfothermic.

Endothermic refers to a reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, resulting in heat being taken in from the surroundings.

12

Is ΔH positive or negative in exothermic reactions?

ΔH is negative in exothermic reactions.

13

Is ΔH positive or negative in endothermic reactions?

In endothermic reactions, ΔH is positive.

14

Is respitation endothermic or exothermic?

Respiration is exothermic.

15

Is the decomposition of calcium carbonate endothermic or exothermic?

The decomposition of calcium carbonate is an endothermic reaction.

16

What name is calcium oxide more commonly known by?

Calcium oxide is known as lime.

17

Is photsynthesis endothermic or exothermic?

Photosynthesis is an endothermic reaction.

18

What is an enthalpy profile diagram used for?

An enthalpy profile diagram is a diagram for a reaction to compare the enthalpy of the reactants with the enthalpy of the products.

19

In the energy profile diagram of an exothermic reaction, which is lower, the reactants or the products?

In the energy profile diagram of an exothermic reaction, the energy of the products is lower than that of the reactants.

20

In the energy profile diagram of an endothermic reaction, which is lower, the energy of the reactants or the products?

In the energy profile diagram of an endothermic reaction, the energy of the reactants is lower than that of the products.

21

Define the activation energy.

Activation energy is the minimum energy required to start a reaction by the breaking of bonds.

22

What symbol represents the activation energy?

EA represents the activation energy.

23

How is the activation energy often supplied?

The activation energy is often supplied by a spark or by heating chemicals.

24

What are the standard conditions?

Standard conditions are a pressure of 100kPa (1 atmosphere), a stated temperature, usually 298K (25oC) and a concentration of 1.0moldm-3 (for reactions with aqueous solutions).

25

What is the pressure used in standard conditions?

The pressure used in standard conditions is 100kPa (1 atmosphere).

26

What is te temperature used in standard conditions?

Standard temperature is usually 298K (25oC).

27

 What concentration is used under standard conditions?

A concentration of 1.0 moldm-3 is used under standard conditions.

28

What symbol represents the standard enthalpy change?

ΔH⊖ is the symbol for the non-specific standard enthalpy change.

29

What do all the components of ΔH represent?

ΔH

  • H is the enthalpy
  • Δ is the change
  • is standard conditions

30

Define the standard state.

The standard state is the physical state of a substance under the standard conditions of 100kPa (1 atmosphere) and 298K (25oC).

31

What is the symbol for the standard enthalpy change of reaction?

The symbol for standard enthalpy change of reaction is ΔHr.

32

Define the standard enthalpy change of reaction.

The standard enthalpy change of reaction, ΔHr, is the enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states.

33

What is the symbol for standard enthalpy change of combustion?

The symbol for standard enthalpy change of combustion is ΔHc.

34

Define the standard enthalpy change of combustion.

The standard enthalpy change of combustion, ΔHc, is the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, all reactants and products being in their standard states.

35

What is the symbol for the standard enthalpy change of formation?

The symbol for the standard enthalpy change of formation is ΔHf.

36

Define the standard enthalpy change of formation.

The standard enthalpy change of formation, ΔHf, of a compound is the enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states under standard conditions

37

What is the symbol that represents the heat exchanged with the surroundings?

Q is the symbol for the heat exchange with the surroundings.

38

What is the relationship that determines the heat exchange with the surroundings?

Q=mcΔT Joules.

39

What do each of the componenets of Q=mcΔT stand for?

Q=mcΔT

Q is the heat exchange with the surroundings

m is the mass of the surroundings involved in the heat exchange

c is the specific heat capacity of the surroundings

ΔT is the temperature change of the surroundings (ΔT = Tfinal - Tinitial)

40

What is the symbol for the specific heat capacity?

c is the specific heat capacity.

41

Define the specific heat capacity.

Specific heat capacity, c, is the energy required to raise the temperature of 1g of a substance by 1oC.

42

If the temperature rises on a thermometer then the reaction is....

If the temperature rises on a thermometer then the reaction is exothermic and ΔH is negative.

43

Why could there be a difference between a data table version of enthalpy hange of combustion and in an experiment carried out?

There could be adifference between data table version of enthalpy change of combustion and in an experiment due to:

  • incomplete combustion
  • heat loss to the surroundings

44

Define bond enthalpy.

Bond enthalpy is the enthalpy change that takes place when breaking by homolytic fission 1 mole of a given bond in the molecules of a gaseous species.

45

Is the breaking of bonds endothermic or exothermic?

Energy is required to break bonds, thus it is endothermic.

46

Is the forming of bonds endothermic or exothermic?

energy is released in the formation of new bonds, so it is exothermic.

47

Define the average bond enthalpy.

Average bond enthalpy is the average enthalpy change that takes place when breaking by homolyitc fission 1 mole of a given type of bond in the molecules of a gaseous species.

48

In an exothermic reaction, which are stronger: the bonds formed or the bonds broken?

In an exothermic reaction the bonds formed are stronger than the bonds broken.

49

In an endothermic reaction, which are stronger: the bonds being formed or the bonds being broken?

In an endothermic reaction, the bonds broken are stronger than the bonds formed.

50

Why is it not always possible to measure the enthalpy change of reaction directly?

It is not always possible to measure the enthalpy change of a reaction directly due to:

  • high activation energy
  • slow reaction rate
  • more than one reaction taking place

51

What is the purpose of Hess' law?

Hess' law provides a method for finding enthalpy chnge of reaction indirectly.

52

What is stated by Hess' law?

Hess' law states that, if a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route.

53

What is an enthalpy cycle?

An enthalpy cycle is a diagram showing alternative routes between reactants and products which allows the indirect determination of an enthalpy change from other known enthalpy changes using Hess' law.

54

Define the rate of reaction.

The rate of reaction is the change in concentration of a reactant or product in a given time.

55

What are the units for rate?

moldm-3s-1

(because it's change in concentration per time)

56

When is the rate of reaction at its fastest?

The rate of reaction is at its fastest at the beginning when the concentration of each reactant is greatest.

57

What does collision theory state?

Collision theory states that a chemical reaction can only take place when reacting molecules collide.

58

Will a reaction take place if there is a head-on collision?

If there is a head on collision, it is more energetic thus a reaction takes place.

59

If there is a glancing blow collision, does a reaction take place?

If there is a glancing blow collision it is less energetic and thus no reaction takes place.

60

Who was the first person to use the term 'catalyst'?

The term 'catalyst' was first used by Jöns Jakob Berzelius.

61

What does a catalyst do?

A catalyst lowers the activation energy of the reaction by providing an alternative route for the reaction to follow.

62

What catalyst is used in the Haber process to make ammonia, NH3?

The Haber process uses an iron catalyst.

63

Which catalyst is used in the contact process to produce H2SO4?

The contact process to produce H2SO4 requires a V2O5 catalyst.

64

Which catalyst is used in the hydrogenation of margarine?

A Ni catalyst is used in the hydrogenation of margarine.

65

How does catalyst development and improvement lead to greater profitability?

Products can be made more quickly and easily, requiring less energy by cutting fuel costs and reducing waste.

66

What was the Ziegler-Natta catalyst important for?

The Ziegler-Natta catalyst was an an important development in the production of non-branched poly(ethene).

67

What is the role of a catalytic converter?

Catalytic converters reduce toxic emissions from vehicles and prevent photochemical smog.

68

Define biocatalysis.

Biocatalysis is any process where the catalyst is an enzyme.

69

What kind of conditions do enzymes operate under?

Enzymes operate under mild conditions such as low temperatures, atmospheric pressure and at an optimum pH value.

70

Define heterogenous catalysis.

Heterogenous catalysis is catalysis of a reaction in which the catalyst has a different physical state from the reactants.

71

Define homogenous catalysis.

Homogenous catalysis is catalysis of a reaction in which the catalyst and the reactants are in the same physical state.

72

What is the Boltzmann distribution?

The Boltzmann distribution is the distribution of energies of molecules at a particular temperature, often shown as a graph. The area under the curve is equal to the total number of molecules in the sample.

73

What is the area under the curve equal to in a Boltzmann distribution?

The area under the curve is equal to the total number of molecules in the sample. The area doesn't change with conditions.

74

What happens to the shape of a Boltzmann districution at higher temperatures?

At higher temperatures, the distribution flattens and shifts to the right, the area is the same as the number of molecules is the same.

75

In what type of system does a dynamic equilibrium exist?

A dynamic equilibrium exists in a closed system.

76

What is stated by Le Chatelier's principle?

Le Chatelier's principle states that when a system in dynamic equilibrium is subjected to a change, the position of equilibrium will shift to minimise the change.

77

If the equilibrium shifts to the right, does that mean more reactants or products are formed?

If the equilibrium shifts to the right that means more products are formed.

78

If the equilibrium shifts to the left, does that mean more reactants or products are formed?

If the equiloibrium shifts to the left, that means more reactants are formed.

79

According to Le Chatelier's principle, increasing the temperature will do what?

Increasing the temperature causes the equilibrium to shift to the direction that decreases the temperature.

80

The nitrogen used in the Haber process is obtained how?

The nitrogen used in the Haber process is obtained by fractional distillation of the air.

81