A student investigated the effect of the size of marble chips on the rate of the reaction between marble chips and hydrochloric acid - AQA - GCSE Chemistry Combined Science - Question 5 - 2018 - Paper 2

The graph shows that as time increases, the volume of gas produced also increases. Initially, the rate of gas production is rapid and it begins to slow down as the reaction proceeds, indicating that the marble chips are being consumed over time.

To find the rate of the reaction at 15 seconds, I would locate the point on the graph corresponding to 15 seconds and note the volume of gas produced at that time. Then, the rate can be determined by calculating the gradient of a tangent line drawn at this point.

The units for the rate of this reaction are cubic centimeters per second (cm³/s).

Smaller marble chips increase the surface area available for the reaction, which leads to a faster reaction rate compared to larger chips.

All marble sizes eventually react completely with the hydrochloric acid, leading to a maximum volume of gas produced which is determined by the amount of acid available.

The surface area of a cube is calculated using the formula:

$ext{Surface Area} = 6 imes ext{side length}^2$

For the large cube with side length 2 cm: $ext{Surface Area} = 6 imes 2^2 = 24 ext{ cm}^2$

Smaller chips have a larger surface area for a given volume, which increases the frequency of collisions between acid particles and the marble chips. This results in a higher reaction rate as per collision theory.

For lower concentration acid, there are fewer acid particles available compared to higher concentration. This leads to fewer successful collisions between acid and marble chip particles, resulting in a slower reaction rate and less gas produced over the same time frame.