a. Exothermic. Heat is released during the burning process.

b. Endothermic. Energy is absorbed by water to change from liquid to vapour phase.

c. Endothermic. Energy is absorbed by ice to change from solid to liquid phase.

For exothermic reactions, the energy absorbed during bond breaking is less than the energy released during bond formation.
Therefore, the bond strength of reactants is much less than the bond strength of products, causing large amounts of energy to be released during explosion.
Gases have a larger volume per mole than solids, thus, the reactants should be in solid state while reactants should be in gaseous state, such that there will be rapid expansion in terms of volume, causing a good explosion.

Temperature is a scale to measure heat energy.
Heat is the vibration of atoms while temperature is the measure of energy.
For example, temperature is the degree of hotness of a cup of coffee while the heat we feel is the transfer of heat energy from the coffee to our hands.

a. The gasoline has the same anti-knocking characteristics as a mixture of 98% iso-octane and 2% heptane.

b. Undetermined. Oxygenates are additives that increase the octane rating. Average fuel containing oxygenates have octane rating of 92 and since 98 is greater than 92, it is highly probable that the fuel contains oxygenates. However, this is not definite.

a. Exothermic. The charcoal combusts with oxygen to form water and carbon dioxide. The energy released of the bond form water and carbon dioxide is greater than the energy required to break the carbon bonds. Heat is released in the process.
b. Endothermic. Water absorbs heat from the body to form water vapour.
c. Endothermic. Ice takes in heat from the surroundings to weaken the hydrogen bonds between the water molecules, so that the water molecules are further apart.

When bonds are broken, energy is absorbed and when bonds are formed, energy is released. For a good explosion, the energy released when the products are formed should be greater than the energy absorbed by the reactants. The overall energy level of the products should be lower than the energy level of the reactants.

Heat is the energy that flows from a hotter to a colder region, while temperature is a measurement of the average speed of molecules decreases.

A practical example is when we leave a cup of hot coffee on the table. Over time, heat is lost to the surrounds, as heat moves from hotter region to a colder region. The temperature of the hot coffee decreases from 100°C to 25°C, as the average speed of molecules decreases.

a. The knocking characteristics of this gasoline is 98% isooctane and 2% heptane.
b. It does not contain oxygenates, as the octane number is lower than 100. The octane rating of oxygenated is usually higher than 100, as oxygenates raises the octane level.

Correct Ans: The octane number does not tell us whether the fuel contains oxygenates.

Process (a) is exothermic because it gives off net heat to the environment as it burns.
Process (B0 is endothermic because water absorbs heat from the skin to overcome its intermolecular bonds which are van der waals forces and hydrogen bondings between the molecules in order to get evaporated into gas molecules.
Process (c) is endothermic because ice absorbs heat from the environment to melt into liquid state.

The bond strength in the product should be significantly greater than that in reactant. This is because for exothermic reaction to occur, the delta enthalpy = |energy of reactant| – |energy of product| < 0. It has been already known that energy is released when bonds are formed to form the product while energy is required to break the bond in the reactant side.

Temperature is a measure of average of the motion of the molecules while heat is the consequence of motion at molecular level.

Set an experiment with 1 hot and 1 cold cup of water separated away from other. Place one hand on the hot cup until no heat can be felt. Then, place the same hand on the cold cup to feel the “coldness”. This feeling of “coldness” is due to the flow of heat from the hot hand to the cold cup of water.

Knocking characteristics of this gasoline is 98% iso-octane and 2% heptane.

We can’t tell whether the fuel does contain oxygenates because octane rating alone does not indicate whether oxygenates are added in.

Endothermic: (b), (c) – Surrounding feels cooler as energy is absorbed. Hydrogen bonds are broken. Van der Waal’s between H and N/O/F that exist % molecules that have hydrogen directly attached to N/O/F.
Exothermic: (a) Heat is produced and we can feel it. Energy released from bonding forming is more than energy released from bond breaking.

Bond strength of products would be strong than the bond strength of reactant such that the enthalpy change of combustion would be higher. Energy level of product is lower and energy level of reactant is higher. Product should be gases instead of liquid and solid.

Temperature is a measurement, not a form of energy and thus cannot be transferred whereas heat is a form of energy that can be transferred from a hotter substance to a colder substance. Heat is produced when water boils and we would need a thermometer to measure the temperature of the water.
Heat – Internal energy of a substance
Temperature – Measure of the amount of energy that a substance contain.

(a) It is 98% isooctane and 2% hexane in terms of knocking charcteristics, where isooctane is assigned a value of 100.
knocking: Preignition -> ignition during compression
(b) We do not know. If we want to know if additives/oxygenates added, we need to look deeper/ find developer.

a. Exothermic – A burning process is releasing heat
b. Endothermic – Water absorbs heat to become water vapour. The H-bonds are also broken in the process
c. Endothermic – Solid ice absorb heat to become liquid.

The bond energy of the reactants are relatively weak and the bond energy of the products are very strong. Thus, more energy is released when the chemical reaction takes place. This will lead to a a negative net energy change, which indicates a large exothermic reaction during an explosion.

Temperature is the property of internal energy : it is the state of the matter(current state).
Heat is the amount of energy transferred between two matters.

For example, if we put ice cubes into a cup of hot coffee, the temperature of the hot coffee will drop and that is due to the heat transfer from the coffee to the ice.

a. Since the premium gasoline has an octane rating of 98, it will burn relatively smoothly. It also indicates that it shows 98% burning properties of iso-octane and 2% of heptane.

b.It has a high possibility to contain oxygenates because normally premium gasoline have a very low octane rating. But it does not give any concrete information/evidence whether there is oxygenates.

a) Exothermic. Heat released as it burns.

b) Endothermic. Water absorbs heat necessary for evaporation, skin feels cooler.

c) Endothermic. Ice absorbs heat necessary for melting.

The relative bond strength of the reactants must be stronger than that of the products.

Solid -> gas very rapidly, releasing energy quick and massive.

Heat: Energy flow from a hotter object to a colder object(motion).

Temperature: Determine the direction of heat flow, and the measure of the average speed of motion.

Example:
Heat.
1 ice on hand VS 5 ices on hand
More contact results in colder
Both case have the same temperature but more heat transferred from hand to 5 ices.

Temperature of hand is higher than ice. Therefore, heat transfers from hand to ice.

a) knocking characteristic of 98% isooctane and 2% of heptane.
– higher ability to burn smoothly without knocking
– more resistant to knocking

b) does not have enough information to know whether it contains oxygenates.

Intermolecular forces are broken.

a. Exothermic
It is exothermic as it releases energy when it burns. It causes us to feel warmer when we are around it.

b. Endothermic
It is endothermic as it absorbs energy to evaporate. When water evaporates from our skin, we tend to feel cold. This is consistent with the fact that endothermic processes causes its surroundings to become colder.

c. Endothermic
It is endothermic as it absorbs energy to melt – it undergoes a change of state from solid to liquid state. This means that bonds were broken between the water molecules in solid state to give rise to a more disordered liquid state. Bond breaking requires energy (it absorbs energy). When we place ice at room temperature, or in room temperature drinks, they absorb the energy of the surroundings and melt. This in turn makes the drinks colder.

For chemical explosions to be exothermic, they have to release energy to its surroundings. This means that the energy used for bond breaking (of the reactants) must be very small and the energy used for bond forming (of the products) is very large; this means the energy released would be a lot. The products of the reaction should be of a lower energy than the reactants. Hence, the products of such exothermic reactions are typically gases.

Heat is the consequence of motion at the molecular level, and temperature is the measure of average speed of the motion. Temperature determines the direction of heat, which flows from a warmer body to a colder body. Heat is a form of energy.

Temperature can be measured directly using a thermometer. However, to measure heat, we need to know the mass, specific heat capacity and temperature of the compound.
When we apply heat to water and the water boils, we can observe bubbles (water vapour). Temperature rises at the same time.

Knocking is the likelihood of the compound undergoing preignition, where the fuel-air mixture ignites before sparking, when compression occurs. It is affected by the different chain lengths.

a. Unlikely to knock as it has a knocking characteristic of 98% isooctane (branched) and 2% heptane (straight-chained). This gasoline behaves like a mixture of these two compounds.

b. Adding oxygenates to gasoline increases the gasoline’s octane rating. Hence, it can be deduced that the fuel contains a good amount of oxygenates.

a. Exothermic, burning gives off heat energy.
b. Endothermic, during evaporation water takes in heat energy and skin feels cooler.
c. Endothermic, during melting ice absorbs heat energy though there’s no change in temperature.

Initial reactant bond strength has to be weak while product bond strength has to be strong to lead to an exothermic reaction. Reactant bond strength is relatively much weaker than product bond strength so that it can be highly exothermic enough to be explosive. Gases are more reactive than solids or liquids due to their weaker bonds.

Heat: total energy (kinetic + potential) possessed by molecules in a piece of matter, measured in joules, and has the ability to do work.
Temperature: not energy, measured in Kelvin, can only be used to measure the hotness or coldness of something.
Eg, during melting, there is no change in temperature, but there is transfer of heat from the surroundings to the ice.

a. It has high anti-knocking characteristics. Higher rating means better for the engine.
b. We do not know. Rating simply corresponds to knocking characteristics and is used as a form of comparison between types of gasoline.

A) Exothermic – Because heat energy is released during the process.
B)Endothermic – Water molecules absorb energy in order to change its state from liquid to gas.
C)Endothermic – Water molecules absorb energy in order to change its state from solid to liquid.

Energy is taken in to break the bond for the reactant. Energy is released when the bond is formed in the product. An explosion requires large amounts of energy to be released. In order to produce a very exothermic reaction, the net energy is produced must be very high. Hence, the bond strength of the product must be a lot higher than that of the reactant.

Temperature is the measurement of heat. Heat is the amount of energy. Higher temperature object will transfer energy to lower temperature object until both has the same amount of energy. Example, temperature of a cup of water and a pail of water could be both 25 degree. but obviously the pail of water has more heat because of its larger mass.

Another difference to note is that temperature has unit of Kelvin(K) while heat has a unit of joules(J).

A) It has a knocking characteristics of 98% octane and 2% ethane.
B) No it does not

a. Exothermic as heat is given out as it burns.
b. Endothermic as water gains energy to change phase from liquid to vapour.
c. Endothermic as it takes in energy for it to melt to overcome the intermolecular forces of attraction between the particles to change into liquid state.

Enthalpy change of reaction = sum of bond strength of bonds broken – sum of bond strength of bonds formed
A good explosion requires a highly exothermic reaction. Thus, the bonds of reactants should be weak and the relative bond strength of the product should be high.

Heat is the total energy of molecular motion in a substance but temperature is a measure of the average energy of molecular motion in a substance. Temperature does not depend on the size and type of the object, but heat does.

For example, the temperature of a small cup of water might be the same as the temperature of a large tub of water, but the tub of water has more heat because it has more water and thus more heat/thermal energy

a. As the reference standard for octane rating is 100, which refers to a gasoline containing pure iso-octane, the gasoline with 98 octane rating has the same knocking characteristics as a mixture of 98% iso-octane and 2% heptane.

b. Oxygenates are chemical compounds that contain oxygen but the octane rating only reflects the knocking characteristics of gasoline but not the chemical formula of it. So the octane rating does not tell us if the fuel contains oxygenates.