Energy From Fuels (SQA National 5 Chemistry): Flashcards
Exam code: X813 75
1/180Still learning
Know0
- FrontEnergy From Fuels
What is an exothermic reaction?
Was this flashcard helpful?
Cards in this collection (18)
What is an exothermic reaction?
An exothermic reaction is one that releases heat energy into the surroundings, causing the temperature of the surroundings to increase.
What is an endothermic reaction?
An endothermic reaction is one that takes in heat energy from the surroundings, causing the temperature of the surroundings to decrease.
True or False?
A temperature decrease in a reaction mixture indicates an exothermic reaction.
False.
A temperature decrease indicates an endothermic reaction, in which heat energy is taken in from the surroundings. A temperature increase indicates an exothermic reaction.
In an exothermic reaction, heat energy is .......... into the surroundings, so the temperature of the reaction mixture .......... .
In an exothermic reaction, heat energy is released into the surroundings, so the temperature of the reaction mixture increases.
What is combustion?
Combustion is a chemical reaction in which a substance reacts with oxygen to release energy. It is an exothermic process and is commonly referred to as burning.
State the two products formed in the complete combustion of a hydrocarbon fuel.
The two products formed in the complete combustion of a hydrocarbon fuel are:
Carbon dioxide (CO2)
Water (H2O)
True or False?
The complete combustion of ethanol produces carbon dioxide and water.
True.
Ethanol contains carbon and hydrogen atoms. During complete combustion the carbon reacts with oxygen to form CO2 and the hydrogen reacts with oxygen to form H2O. The balanced equation is: C2H5OH + 3O2 → 2CO2 + 3H2O.
State the correct order of steps for balancing a combustion equation.
The correct order of steps for balancing a combustion equation is:
Balance the carbon atoms first
Then balance the hydrogen atoms
Finally balance the oxygen atoms
Combustion is an .......... reaction because heat energy is .......... into the surroundings when a fuel burns.
Combustion is an exothermic reaction because heat energy is released into the surroundings when a fuel burns.
What is calorimetry?
Calorimetry is a technique used to measure the quantity of heat energy released by a burning fuel by using it to raise the temperature of a known mass of water.
State the two measurements required when carrying out a simple calorimetry experiment.
The two measurements required in a simple calorimetry experiment are:
The mass of water being heated (m)
The temperature change of the water (ΔT)
In calorimetry, the formula .......... is used to calculate the heat energy released, where c is the .......... of the substance being heated.
In calorimetry, the formula Eh = cmΔT is used to calculate the heat energy released, where c is the specific heat capacity of the substance being heated.
True or False?
In the calorimetry formula Eh = cmΔT, the mass of water must be in grams.
False.
The mass of water must be in kilograms (kg). To convert grams to kg, divide by 1000. Using grams instead of kg is a common exam error.
What is the value of the specific heat capacity of water (c) used in the calorimetry formula, and where is it found?
The specific heat capacity of water is 4.18, found in the SQA Data Booklet. It is used in the formula Eh = cmΔT.
A fuel heats 200 g of water from 20 °C to 50 °C. Calculate the heat energy absorbed by the water.
Eh = cmΔT
Eh = 4.18 × 0.2 × (50 − 20)
Eh = 4.18 × 0.2 × 30 = 25 kJ
True or False?
The unit of Eh in the formula Eh = cmΔT is joules (J).
False.
When mass is in kg and c = 4.18, the unit of Eh is kilojoules (kJ), not joules. This is a common source of exam errors.
To calculate the temperature change in Eh = cmΔT, use the formula ΔT = .......... minus .......... .
To calculate the temperature change in Eh = cmΔT, use the formula ΔT = T(final) minus T(initial).
50.16 kJ of heat energy was transferred to 1.2 kg of water. Calculate the temperature change of the water.
Eh = cmΔT, so ΔT = Eh ÷ (c × m)
ΔT = 50.16 ÷ (4.18 × 1.2)
ΔT = 10 °C
Sign up to unlock flashcards
or