a. Exothermic. We are able to feel the heat radiating from the charcoal.
b. Endothermic. Evaporation is an endothermic process heat is taken away.
c. Endothermic. Heat energy is absorbed to melt the ice. Hydrogen bonds are broken and water molecules are allowed to move about freely.

Bond strength of the reactants has to be weaker and easy to break while bond strength of products needs to be stronger. Volume changes rapidly as gases are produced.

Heat is the flow of energy from hotter to less hot body while temperature is the measure of average speed of heat.

E.g. Energy from hot milo is transferred to colder ice cubes. Temperature will be between initial temperature of ice and milo.

a. 98% of iso-octane and 2% heptane.
b. No. Octane rating only gives information about knocking characteristics.

a. Exothermic reaction as we feel warm due to heat release. b. Endothermic reaction as we feel cold since heat is absorbed. c. Endothermic reaction as we feel cold since heat is also absorbed.

reactant should have a weaker bond strength compared to its products for a good explosion since more energy is released when a strong bond is formed while less energy is needed to break a weak bond. Gas also give good explosions.

temperature is a measurement while heat is a form of energy that flows from a better to cooler region.

4a. It has 98% Isoctane while 2% of heptane. b There is a hih possibility of it containing oxygenate as it reduceds knocking

a. Exothermic – Heat Energy is release so that bonds can be formed.
b. Endothermic
c. Endothermic
Heat energy is absorbed in both B & C so that hydrogen bonds can be broken.

The relative bond strengths in the reactants and products needs to be weak so that bonds can be broken easily. For example, elements in gaseous state generally have weaken bonds thus it would be idea for a good explosion.

Heat is energy that flows from a hotter to a colder object while temperature determines the direction of heat flow.Heat is a consequence of motion at the molecular level; temperature is a measure of the average speed of that motion.The heat of an object contains is the amount of its thermal energy, measured in joules or J. On the other hand, the temperature of an object is to do with how hot or cold it is, measured in degrees Celsius. Note that the unit of temperature is written as °C.

For example, to boil water we must increase its temperature to 100°C. It takes longer to boil a large beaker of water than a small beaker because the large beaker contains more water and needs more thermal energy to reach 100°C.

a. Octane rating measures the ability of gasoline to burn smoothly without knocking. Octane number of 92 means a knocking characteristic of 98% isooctane and 2% heptanea.

b. The rating is just an indication of the composition of fuel. It does not give an accurate description on whether oxygenates are present. Thus, further analysis is required to determine its oxygenates level.

A: Exothermic – Heat energy is release so that bond can be formed
B: Endothermic
C: Endothermic
Heat energy is absorbed in both B & C as energy is needed to break the hydrogen bond.

The relative bond strengths in both reactants and product should be weak so that it is easier for the elements to break bond, preferably in gaseous state since these elements usually have weaker bond.

Heat is energy that flows from a hotter to a colder object while temperature determines the direction of heat flow. Heat is a consequence of motion at the molecular level and temperature is a measure of the average speed of that motion. The heat of an object contains is the amount of its thermal energy, measured in joules or J. On the other hand, the temperature of an object is to do with how hot or cold it is, measured in degrees Celsius. Note that the unit of temperature is written as °C.

For example, to boil water we must increase its temperature to 100°C. It takes longer to boil a large beaker of water than a small beaker because the large beaker contains more water and needs more thermal energy to reach 100°C.

a. Octane rating measure of the ability of gasoline to burn smoothly without knocking. Octane number of 98 means a knocking characteristic of 98% isooctane and 2% heptane.

b. The rating is just a ratio of the composition of the fuel. Hence it does not give an accurate description on whether oxygenates are present. Further analysis is required to determine its actual oxygenates level.

1a) Exothermic: Charcoal briquette releases heat when it burns

1b) Endothermic: Water absorbs heat needed for evaporation by breaking bonds (H-bonding)

1c) Endothermic: (solid) –> (liquid) Ice absorbs heat so as to allow it to melt. When ice absorbs heat as energy, it gains kinetic energy until it reaches its melting point where it will exist as a liquid.

An example of a good explosion: methane combustion.

CH4 + 2 O2 –> CO2 + 2 H2O

For the reaction to be exothermic, the net change of energy must be negative i.e. the energy absorbed to break the bond must be less than the energy released during bond formation. The bond energies of the products should be larger than those of reactants.

In methane combustion, the bond energies involved are: C-H: 416KJ/mole, O=O: 498KJ/mole, H-O: 467KJ/mole and C=O: 803KJ/mole

Bond energies of reactants = 4 C-H + 2 O=O = 4 X 416 + 2 X 498 = +2660KJ/mole
Bond energies of product = 2 C=O + 4 O-H = 2 X 803 + 4 X 467 = -3474KJ/mole

Net change = 2660 – 3474 = -814KJ/mole

The bond energies of the product > bond energies of the reactant. Hence, net energy change is negative (as shown above). This indicates a large exothermic reaction.

Heat = energy transfer.
e.g. touching a hot coffee.

Saying that a hot coffee has “heat” = wrong.
A better statement = “This coffee can transfer energy as heat towards the lower energy (finger).”

Heat depends on the speed of particles; the number of particles and the type of particles in an object whereas temperature does not depend on size or type of object. Temperature is an intensive property.

e.g. when you boil eggs
You need X amount of water at 100-degree Celsius for you to cook one hard boiled egg. However, you will need either/both more than X amount of water or/and more time to cook two or more hard boiled eggs.

Octane rating = The measure of the ability of the gasoline to burn smoothly without knocking.

a) 98% isooctane + 2% heptane

b) It does not indicate if the fuel contains oxygenates

a. Exothermic, as charcoal briquette releases heat as it burns.
b. Endothermic, as the water absorbs the heat necessary for evaporation.
c. Endothermic, as heat is absorbed from the environment to break the bonds of ice.

The bond energies of the products are larger than these of the reactants. This will lead to a large negative energy change, indicating an exothermic reaction.

Temperature is a form of measurement to indicate how heat flows while heat is a form of energy. Heat flows from a hotter object to a cooler object. Hence, an example would be, pouring hot water to a cup of cold water. The heat from the hot water will flow to the cold water and the final temperature will be a mixture between the two solutions.

a. Gasoline with an octane rating is composed of 98% isooctane and 2% n-heptane. As it is a ‘premium gasoline’, it has a high resistance to knocking.
b. Octane rating does not contain any information pertaining to the fuel containing oxygenates or not. Other labels around the pump will contain this information.

(a) exothermic- a charcoal briquette releases heat as it burns
(b) endothermic- water absorbs the heat necessary for evaporation from your skin, and your skin feels cooler.
(c) endothermic- ice absorbs the necessary heat to melt from the environment.

weak bond strengths for reactants, strong bond strength for products, and in doing so, the overall reaction becomes a very exothermic one. Less energy is taken in to break weak bonds, and more energy released to form strong bonds.

Heat is the energy that flows from a hotter to a colder object; consequence of motion at the molecular level. Temperature determines the direction to which heat flows (degree of hotness and coldness); average speed of that motion.

Heat from the fire cooks the food.
Temperature is the measurement of the day’s weather, and it tells us of the degree to which the temperature changes at different time intervals.

(a) It has a knocking characteristic of 98% isooctane, and 2 % hectane, which makes it 98% resistant to knocking, which is great.
(b) No, if there is a need to find out, we can’t be looking purely at octane ratings.

A. Exothermic. Heat is released when charcoal briquette burns.
B. Endothermic. Heat is absorbed for water to evaporate and hydrogen bonding between water molecules are broken.
C. Endothermic. Heat is absorbed and required to reach the melting point of ice.

Heat is released from forming bonds and heat is absorbed to break bonds. For an exothermic reaction, heat is released. Therefore, heat released during bond formation (products) is greater that the heat absorbed for bond breaking (reactants). Hence the product would have a greater bond strength than the reactants and the products are more stable.

Heat is the energy that flows from the hotter object to the colder object, it is the consequence of motion at the molecular level whereas temperature is a measure of the average speed of that motion.

A practical example would be a hot cup of coffee cooling down. As it cools gradually, heat from the coffee is transferred to the surrounding air which is at a lower temperature. The rate at which heat transfers is the temperature. Temperature difference causes heat to flow from the hotter region to cooler region.

A. Octane rating of 98 means a knocking characteristic of 98% isooctane and 2% heptane.

B. Octane rating measures the ability of gasoline to burn smoothly without knocking. Fuels that contain oxygenates generally have a higher octane rating. The higher the octane rating, the higher possibility that it contains oxygenates. Octane rating does not tell us whether oxygenates are present or not but only the likelihood.

a) Exothermic – Burning releases energy in the form of heat.

b) Endothermic – Water absorbs heat energy before evaporation occurs.

c) Endothermic – Ice absorbs heat energy, this will cause the ice to melt into liquid due to the rise in temperature. This breaks the intermolecular forces of attraction, such as hydrogen bonding and van der waals, between water molecules.

The reactants will have lower bond strength, whereas the products will have higher bond strength, in order for an exothermic reaction to occur.

Heat is energy that flows from a hotter to a colder region, whereas temperature determines the direction of heat flow. Heat is due to the motion of molecules while temperature is a measure of the average speed of the motion.

a) It has similar knocking resistance as octane.

b) The higher the concentration of oxygenates in the fuel, the higher the octane ratings, which will allow the engine to run more smoothly.

1a) Heat is released when the charcoal burns hence the process is exothermic.
1b) Heat is taken in by the water molecule to change its state to a gaseous form, thus it is an endothermic process
1c) Heat is taken into the ice to melt into water.

Heat is released when bonds are formed and heat is absorbed when bonds are broken. For exothermic reactions, heat is released.Thus, the heat released by the overall reaction must be more than the heat needed to break the bonds for it to become an exothermic reaction.When the bond strength of the product is high, the stability of the products increases and so does the yield. A good explosion will require the very rapid release of heat energy in a very short time, coupled with an expansion of mass rapidly as well.

My friend, heat is the energy that flows from a hotter object to a colder object. It is the consequence of motion at the molecular level. Temperature is a measure of the average speed of the motion, a measurement of how much heat is there by an integer. Like a hot cup of coffee cooling down on the table, heat from the coffee is transferred to the surrounding. The temperature gradually averages with the coffee.

a) Octane rating of 98 means a knocking characteristic of 98% iso-octane and 2% heptane. The rating often measures the ability of the gasoline to burn smoothly without knocking.
b) The higher the octane rating the higher the possibility that it contains oxygenates, it does not provide a definite answer to whether oxygenates are present but a probability.