At 37 deg C, the enzymes in yeast are the most active, so fermentation process will be fastest.
At low temperatures, the enzymes in yeast are inactive, so fermentation will be slow.
At high temperatures, the enzymes in yeast will be denatured, so fermentation will stop.
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Movement of electrons in discharge ball
An electrostatic generator is used to produce sparks as shown below.
The belt carries negative charges to the dome, making it negatively charged. Before a spark is produced, the discharge ball becomes positively charged.
Describe and explain the movement of electrons in the discharge ball and in the conducting rod as the ball becomes charged.
The electrons in the discharge ball and in the conducting rod moves downwards through the conducting wire, and to the ground.
Electrostatic charging by induction occurs in the ball and rod as they are placed near to the negatively charged dome. Like charges repel, causing the negatively charged electrons in the ball and rod to move away from the dome, escaping through the conducting wire to the ground.
Movement of air particles in sound waves
A sound wave in air is illustrated below.
Points A, B, C and D are all the centers of regions of compression in the sound wave.
Describe what happens as one complete sound wave moves past a point.
The particles in the air are disturbed by the sound waves and vibrates to and fro, in a direction parallel to the direction of the sound waves.
An air particle in the sound wave will vibrate from its rest position to the left, until it reaches its maximum displacement to the left, then vibrate towards the right, move past its rest position, until it reaches its maximum displacement to the right. Then it vibrates to the left, until it returns back to its original rest position to complete one wave motion of the sound wave.
What is an addition reaction?
An addition reaction is a reaction in which new atoms are added to the organic compound by converting carbon-carbon double covalent bonds to carbon-carbon single covalent bonds.
Differences between boiling and evaporation
| Boiling | Evaporation |
| Occurs at a fixed temperature | Occurs at any temperature below boiling point |
| Quick process | Slow process |
| Takes place throughout the liquid | Takes place at the surface of the liquid |
| Bubbles form | No bubbles |
| Temperature remains constant | Temperature may vary |
| Thermal energy supplied by energy source | Thermal energy supplied by surroundings |
What is a homologous series?
A homologous series is a family of organic compounds with:
– same functional group
– same general formula
– similar chemical properties
– gradual change in physical properties
Examples of homologous series:
– Alkanes
– Alkenes
– Alcohols
Advantages and Disadvantages of a Thermocouple Thermometer
| Advantages | Disadvantages |
| Can measure a wide range of temperature, from -100 deg C to 2500 deg C | Low sensitivity to small temperature changes |
| Can measure temperature at a point | Relatively low accuracy, degree of error is 1 deg C to 2 deg C |
| Rugged, not easily damaged | Prone to corrosion, due to two metals of different reactivity being in contact |
| Respond quickly to temperature changes | Low voltage output, which makes the output easily distorted by interference from nearby electronic devices. |
What is “inertia”?
Inertia refers to the reluctance of the object to change its state of rest or motion.
The bigger the mass of a body, the greater its inertia.
(ie, the bigger the mass, the more difficult it is to make a stationary object move, or to make a moving object change its speed or direction, due to its inertia)
State the Principle of the Conservation of Energy
The Principle of the Conservation of Energy states that energy cannot be destroyed or created.
It can only be converted from one form to another, or transferred from one body to another.
The total energy in the system remains constant.
Describe the structure of metals and metallic bonds.
The structure of metal consists of positive metal ions, arranged in a regular pattern, floating in a sea of delocalized electrons.
Metal atoms have the tendency to lose their valence electrons to form positive ions.
These valence electrons become delocalized and form a ‘sea of mobile electrons’ around the positive ions.
The strong electrostatic force of attraction between the positive metal ions and delocalized electrons form strong metallic bonds.
The layers of metal ions can slide over one another when sufficient force is applied.
