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topic 5 - energy changes Flashcards

1
Q

What are cells in the context of chemistry?

A

Cells contain chemicals that react to produce electricity.

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2
Q

What factors affect the voltage produced by a cell?

A

The voltage produced by a cell depends on several factors including the type of electrode and the electrolyte used.

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3
Q

How is a simple cell made?

A

A simple cell can be made by connecting two different metals in contact with an electrolyte.

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4
Q

What defines a battery in electrochemistry?

A

A battery is defined as two or more cells connected together in series to provide a greater voltage.

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5
Q

What happens in non-rechargeable cells?

A

In non-rechargeable cells chemical reactions stop when one of the reactants has been used up.

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6
Q

What is an example of a non-rechargeable battery?

A

Alkaline batteries are a common example of non-rechargeable batteries.

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7
Q

What distinguishes rechargeable cells from non-rechargeable ones?

A

Rechargeable cells can be recharged because the chemical reactions are reversed when an external electrical current is supplied.

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8
Q

What is a fuel cell?

A

A fuel cell is a device that is supplied by an external source of fuel such as hydrogen and oxygen or air and oxidizes the fuel electrochemically to produce electricity.

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9
Q

What is the overall reaction in a fuel cell?

A

The overall reaction in a fuel cell is the oxidation of fuel which takes place electrochemically to generate a potential difference.

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10
Q

What type of fuel is commonly used in fuel cells?

A

Hydrogen is commonly used as a fuel in fuel cells.

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11
Q

What is the role of the electrolyte in a cell?

A

The electrolyte allows the movement of ions and facilitates the chemical reactions that produce electricity.

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12
Q

What happens when one of the reactants is used up in a non-rechargeable battery?

A

When one of the reactants is used up in a non-rechargeable battery the chemical reactions stop and the battery can no longer produce electricity.

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13
Q

Can batteries be connected in series and why?

A

Yes batteries can be connected in series to increase the total voltage output.

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14
Q

What is the primary action in a rechargeable cell when it is charged?

A

The primary action in a rechargeable cell during charging is the reversal of the chemical reactions that occurred during discharge.

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15
Q

What types of reactions occur within a fuel cell?

A

Oxidation reactions occur within a fuel cell resulting in the production of electrical energy.

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16
Q

How does the voltage change with different types of electrodes in a cell?

A

Different types of electrodes produce different voltages due to their electrochemical properties leading to variations in the potential difference of the cell.

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17
Q

What is required for the operation of a fuel cell?

A

A continuous supply of fuel such as hydrogen and an oxidizer such as oxygen or air are required for the operation of a fuel cell.

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18
Q

What is the significance of external electrical current in rechargeable batteries?

A

The external electrical current is significant because it enables the chemical reactions within rechargeable batteries to reverse allowing them to be reused.

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19
Q

What is hydrogen fuel cell technology?

A

Hydrogen fuel cell technology involves the oxidation of hydrogen to produce water creating energy in the process. It serves as a potential alternative to traditional rechargeable cells and batteries.

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20
Q

How do hydrogen fuel cells differ from rechargeable batteries?

A

Hydrogen fuel cells can operate continuously as long as fuel is supplied. In contrast rechargeable batteries can be recharged by reversing the chemical reaction meaning they do not require a constant supply of fuel.

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21
Q

What are the advantages of using hydrogen fuel cells?

A

Advantages include continuous operation (as long as fuel is available) high energy density and the only major byproduct being water.

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22
Q

What are the disadvantages of hydrogen fuel cells?

A

Disadvantages include storage challenges as hydrogen is a gas that needs to be kept at high pressure transportation difficulties and disposal issues since fuel cells are non-biodegradable.

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23
Q

What is produced when hydrogen is burned?

A

When hydrogen is burned it reacts with oxygen to produce water as the only byproduct.

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24
Q

What are the half-equations at the anode and cathode in a hydrogen fuel cell?

A

At the anode (positive electrode): H₂(g) → 2e⁻ + 2H⁺(aq). At the cathode (negative electrode): 4H⁺(aq) + O₂(g) + 4e⁻ → 2H₂O(g).

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25
What does an exothermic reaction entail?
An exothermic reaction is a chemical reaction that releases energy usually in the form of heat or light.
26
What does an endothermic reaction entail?
An endothermic reaction is a chemical reaction that absorbs energy from its surroundings often causing a drop in temperature.
27
What is the principle of energy conservation in chemical reactions?
The principle of energy conservation states that the total amount of energy in the universe remains constant during chemical reactions; energy can neither be created nor destroyed only transformed.
28
How does the storage of hydrogen impact its use as a fuel?
Hydrogen as a gas requires high-pressure storage which complicates transportation and storage logistics.
29
What environmental impact does burning hydrogen have?
Burning hydrogen produces water vapor as a byproduct making it a cleaner alternative to fossil fuels that release carbon dioxide and other pollutants.
30
What is the significance of the pH values for H⁺ ions in a hydrogen fuel cell?
The concentration of H⁺ ions (or protons) in solution can affect the reactions at the electrodes impacting efficiency and overall cell performance.
31
What factors affect the efficiency of hydrogen fuel cells?
Factors affecting efficiency include temperature pressure the type of electrolyte used and the purity of hydrogen and oxygen gas.
32
How is hydrogen typically produced for fuel cells?
Hydrogen can be produced through various methods including steam methane reforming electrolysis of water and gasification of biomass.
33
Discuss the role of catalysts in hydrogen fuel cells.
Catalysts in hydrogen fuel cells typically platinum-based increase the rate of reaction at the electrodes enhancing efficiency by allowing reactions to occur at lower temperatures.
34
What are some current applications of hydrogen fuel cell technology?
Current applications include fuel cell vehicles (like cars and buses) portable power generators and stationary power systems in remote areas.
35
What occurs at the beginning and end of a chemical reaction in terms of energy transfer?
The energy at the beginning is the same as at the end of a chemical reaction which means if a reaction transfers energy to the surroundings the product molecules must have less energy than the reactants by the amount transferred.
36
Define exothermic reactions. Give examples.
An exothermic reaction is one that transfers energy to the surroundings leading to an increase in the temperature of the surroundings. Product molecules must have less energy than the reactants by the amount transferred. Examples include combustion many oxidation reactions and neutralization. Everyday examples are self-heating cans and hand warmers.
37
What happens to the temperature of surroundings in an exothermic reaction?
In an exothermic reaction the temperature of the surroundings increases due to the transfer of energy from the reactants to the surroundings.
38
What are the energy characteristics of reactants and products in an exothermic reaction?
In an exothermic reaction the product molecules have less energy than the reactants by the amount of energy that has been transferred to the surroundings.
39
Define endothermic reactions. Provide examples.
An endothermic reaction is one that takes in energy from the surroundings leading to a decrease in the temperature of the surroundings. Product molecules must have more energy than the reactants. Examples include thermal decomposition and the reaction of citric acid with sodium hydrogen carbonate.
40
What is the effect of an endothermic reaction on the temperature of the surroundings?
In an endothermic reaction the temperature of the surroundings decreases because energy is absorbed from the surroundings.
41
What must be true about the energy of reactants and products in an endothermic reaction?
In an endothermic reaction the product molecules must have more energy than the reactants.
42
What are some practical applications of endothermic reactions?
Some sports injury packs are based on endothermic reactions which provide a cooling effect.
43
What is a common everyday example of an exothermic reaction?
Self-heating cans for food and beverages such as coffee and hand warmers are common everyday examples of exothermic reactions.
44
What type of reaction is thermal decomposition considered?
Thermal decomposition is considered an endothermic reaction because it requires heat to break down the substances involved.
45
What is the relationship between reactants and products in terms of energy for exothermic and endothermic reactions?
In exothermic reactions reactants have more energy than products with energy released to the surroundings. In endothermic reactions reactants have less energy than products with energy absorbed from the surroundings.
46
What is necessary for a chemical reaction to occur between reacting particles?
Reacting particles must collide with each other and with sufficient energy.
47
What is the definition of activation energy in the context of chemical reactions?
Activation energy is the minimum amount of energy that particles must have to react.
48
What information can reaction profiles provide about a chemical reaction?
Reaction profiles can show the relative energies of reactants and products the activation energy and the overall energy change of a reaction.
49
How can you determine if a reaction is exothermic or endothermic using a reaction profile?
You can tell if a reaction is exothermic or endothermic by comparing the energies of reactants and products; if products are lower on the energy scale than reactants it is exothermic and if products are higher it is endothermic.
50
What happens to energy in an exothermic reaction?
In an exothermic reaction heat is released to the surroundings resulting in products having less energy than the reactants.
51
What happens to energy in an endothermic reaction?
In an endothermic reaction heat is taken in from the surroundings leading to products having more energy than the reactants.
52
What is the role of energy in breaking bonds during a chemical reaction?
Energy must be supplied to break bonds in the reactants during a chemical reaction.
53
What occurs regarding energy when bonds are formed in products?
Energy is released when bonds in the products are formed.
54
Can the energy needed to break bonds and the energy released when bonds are formed be calculated?
Yes both the energy needed to break bonds and the energy released when bonds are formed can be calculated.
55
What does a vertical reaction profile indicate about the energy levels of reactants and products?
A vertical reaction profile shows the difference in energy between reactants and products as well as the activation energy.
56
What is the significance of the energy scale on a reaction profile?
The energy scale indicates the relative energy levels of the reactants products and the activation energy required for the reaction to proceed.
57
Describe an exothermic reaction in terms of energy changes.
In an exothermic reaction the energy of the products is lower than that of the reactants indicating that energy is released to the surroundings.
58
Describe an endothermic reaction in terms of energy changes.
In an endothermic reaction the energy of the products is higher than that of the reactants indicating that energy is absorbed from the surroundings.
59
How do reaction profiles help in predicting the outcomes of chemical reactions?
Reaction profiles provide insight into activation energies and overall energy changes helping predict whether a reaction will release or absorb energy.
60
What is bond energy?
Bond energy is the amount of energy required to break one mole of bonds in gaseous molecules; it is a measure of bond strength.
61
What is the overall energy change in a chemical reaction involving bond breaking and forming?
The overall energy change can be calculated by taking the sum of energy taken in to break bonds and subtracting the sum of energy released to form bonds.
62
Define endothermic reaction with respect to bond energies.
An endothermic reaction is a reaction that absorbs energy from the surroundings leading to an overall energy intake. In terms of bond energies it occurs when the energy taken in to break bonds is greater than the energy released when forming new bonds.
63
Define exothermic reaction with respect to bond energies.
An exothermic reaction is a reaction that releases energy to the surroundings resulting in an overall energy release. This occurs when the energy released when forming bonds is greater than the energy taken in to break bonds.
64
What happens to the energy balance in an endothermic reaction?
In an endothermic reaction more energy is required to break reactant bonds than is released when product bonds are formed resulting in a net intake of energy.
65
What happens to the energy balance in an exothermic reaction?
In an exothermic reaction more energy is released when product bonds are formed than is required to break reactant bonds resulting in a net release of energy.
66
How do you calculate the overall energy change of a reaction?
Overall energy change = (Sum of bond energies of bonds broken) - (Sum of bond energies of bonds formed).
67
What is the significance of bond energies in chemical reactions?
Bond energies are critical for predicting whether a reaction is endothermic or exothermic and understanding the stability of reactants and products.
68
Can you provide an example of a reaction that is endothermic?
A common example of an endothermic reaction is the process of photosynthesis where plants absorb energy from sunlight to convert carbon dioxide and water into glucose.
69
Can you provide an example of a reaction that is exothermic?
An example of an exothermic reaction is combustion such as the burning of methane (CH4 + 2O2 -> CO2 + 2H2O) which releases energy in the form of heat.

Chemistry (10 decks)

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